R dataset
Motivation for this pull request came from this problem: http://stackoverflow.com/q/19039356/190597.

The problems:
- `pandas.rpy.common.load_data`  currently fails to load high-dimensional arrays such as the "Titanic" dataset. `load_data` prints an error to stdout and returns None.
- Applying `load_data` to "iris3", "state.division" or "state.region" R datasets currently raise a TypeError.
- Timeseries R data is currently converted to lists that lack a time series index.
- Factor data is  converted to a list of index numbers without any levels information.

This pull request:
- Provides code which allows `load_data` to convert the "Titanic" dataset (and similar high-dimensional arrays) to "melted" DataFrames. The code _does not_ use R's melt function, since that would introduce a new dependency.
- load_data now returns a DataFrame for arrays like "iris3".
- load_data converts R factors like "state.division" and "state.region" to lists which use the levels as values.
- load_data converts ts (timeseries) R data, like "airmiles" to Series with an index showing the times. Note however I wasn't able to convert the index to a DatetimeIndex since the same code is used to convert numeric R data (like "euro") which does not have a time-related index.
- moves already existant tests from rpy/common.py to tests/test_rpy.py
- adds new unit tests which highlight the problems mentioned above, and tests for what I think is more desireable behavior as described above.

add rpy2 in ci/requirements

2.7, 3.3 maybe
 i think need to add `R` in `ci/install.sh` as well
 problem is that is a huge honking install on ubuntu
 all this for `r-base` on ubuntu 12.04:

```
autoconf automake autotools-dev cdbs dh-translations dpatch fakeroot fontconfig fontconfig-config intltool libbz2-dev libcairo2 libdatrie1 libencode-locale-perl libfile-basedir-perl libfile-desktopentry-perl
libfile-listing-perl libfile-mimeinfo-perl libfont-afm-perl libfontconfig1 libfontenc1 libgl1-mesa-dri libgl1-mesa-glx libglapi-mesa libhtml-form-perl libhtml-format-perl libhtml-parser-perl
libhtml-tagset-perl libhtml-tree-perl libhttp-cookies-perl libhttp-daemon-perl libhttp-date-perl libhttp-message-perl libhttp-negotiate-perl libice6 libio-socket-inet6-perl libio-socket-ssl-perl libllvm3.0
liblwp-mediatypes-perl liblwp-protocol-https-perl libmailtools-perl libncurses5-dev libnet-http-perl libnet-ssleay-perl libpango1.0-0 libpaper-utils libpaper1 libpcre3-dev libpcrecpp0 libpixman-1-0 libsm6
libsocket6-perl libthai-data libthai0 libtiff4 liburi-perl libutempter0 libwww-perl libwww-robotrules-perl libx11-xcb1 libxaw7 libxcb-glx0 libxcb-render0 libxcb-shape0 libxcb-shm0 libxcomposite1 libxcursor1
libxdamage1 libxfixes3 libxft2 libxi6 libxinerama1 libxml-parser-perl libxmu6 libxpm4 libxrandr2 libxrender1 libxss1 libxt6 libxtst6 libxv1 libxxf86dga1 libxxf86vm1 m4 patchutils python-scour r-base-core
r-base-dev r-base-html r-cran-boot r-cran-class r-cran-cluster r-cran-codetools r-cran-foreign r-cran-kernsmooth r-cran-lattice r-cran-mass r-cran-matrix r-cran-mgcv r-cran-nlme r-cran-nnet r-cran-rpart
r-cran-spatial r-cran-survival r-doc-html r-recommended shared-mime-info tcl8.5 tk8.5 ttf-dejavu-core unzip x11-common x11-utils x11-xserver-utils xbitmaps xdg-utils xterm zip
```
 any way to have it skip all of the display stuff ?
 someone more knowledgeable than me about `apt-get` may know the answer to that question. @yarikoptic can you grace us with your debian wisdom? is something like this possible?
 It's simply not the case that all of those deps are required to install R. On Arch Linux, these are the dependencies:

blas  lapack  bzip2  libpng  libjpeg  libtiff  ncurses  pcre  readline  zlib  perl  gcc-libs  libxt  libxmu  pango  xz  desktop-file-utils
 why do you need to build R, can't you just use apt-get to get the package
without build-dep?

On Sun, Sep 29, 2013 at 12:12 AM, Phillip Cloud notifications@github.comwrote:

> It's simply not the case that to build R this is required. On Arch Linux,
> these are the following dependencies:
> 
> blas  lapack  bzip2  libpng  libjpeg  libtiff  ncurses  pcre  readline  zlib  perl  gcc-libs  libxt  libxmu  pango  xz  desktop-file-utils
> 
> —
> Reply to this email directly or view it on GitHubhttps://github.com/pydata/pandas/pull/5036#issuecomment-25314107
> .
 those ubuntu deps i listed above _are_ from calling `apt-get`, shouldn't have said "build". meant "install"
 well -- it feels that list a bit bloated due to recommends -- what if you do `apt-get install r-base --no-install-recommend`?  that still would need `x11-common xdg-utils` though, but most probably that is unavoidable... I would recommend on your box to run  `sudo apt-get install debtree; debtree --no-recommends r-base | dot -Tsvg > /tmp/r-basedepends.svg; firefox /tmp/r-basedepends.svg` which would give you a nice graph of dependencies so you could clearly see how they are pulled in.
 Installing R on Travis seems like an unsolved problem for many people: http://yihui.name/en/2013/04/travis-ci-general-purpose/. Would it be helpful if I move the unit tests back into rpy/common.py so those with R installed could run the tests, but not have it part of the official test suite?
 just add a `raise nose.SkipTest("R not installed")` at the top of the file
instead. (and, you know, check for that too :))
