Parse raised exceptions and their error messages sans interpolation/format spec
This PR partially addresses #3024. It also provides a shiny new script useful looking at the current state of the messages in raised exceptions. Here's an example of some output:
# Example

![pandas-shiny-new-parse-asserts](https://f.cloud.github.com/assets/417981/457480/70282b60-b39e-11e2-8db1-f5cfb4f0c5bf.png)

You can reproduce this with

``` sh
scripts/parse_except.py --type empty --module pandas --kind assert
```

from the top level pandas directory.
# Description

The above line searches for all empty raises in the module `pandas` whose constructor matches the regular expression `'.*assert.*'`--not case sensitive.

Note: **This assumes you have installed pandas with `python setup.py develop`**. This will not work without that (well, that's not strictly true, but it will search for pandas code that's installed wherever you installed it `/usr/*/site-packages/*/pandas` or `$VIRTUAL_ENV/*/pandas`, for example, which is probably not what you want).

To see all of the options and a short description you can do the usual:

``` sh
scripts/parse_except.py --help
```

This could probably use a `NodeVisitor` subclass...but I wanted to hack this together before optimizing.
 @jreback this could be merged if y'all think it's useful...all the nan's in the above pic are gone now since i filled all those missing or vague assert messages in and a few others as well. rls notes here?
 @jreback @y-p i will close this if there's no chance of it getting in. no sense in keeping things open unnecessarily...
 I didnt' realize you changed a bunch of no-message AssertionErrors.....so this is good...

does this pass travis?
 > I didnt' realize you changed a bunch of no-message AssertionErrors.....so this is good...

i was hoping that the script would be useful (alas, i probably spent too much time creating the assertion-table-lister thing because i think asts are fun) it should pass...it wasn't before because i did 1e9 rebases in a row and travis doen't like that
 @cpcloud 
you might want to join pandas-dev ml:

http://mail.python.org/mailman/listinfo/pandas-dev
 this passes
