ENH/API: Keep original traceback in DataFrame.apply
When "raise <exception instance>" is used inside a try/except block, the
original stacktrace (containing the code path that raised the original
exception).  This makes debugging difficult since all we know is that an error
occured when `frame._apply_standard` attempted to call the provided function.
Preserve the original stacktrace by using "raise" instead of "raise <exception
instance>".  This facilitates debugginb by allowing us to see where (in the
provided callable) the exception occured.

can you set up travis ci and add a test? thx
 I set up Travis CI, but it won't run until I push a new commit (which I'll do once I add a test).  As for the test, do you have any pointers on how one might be able to test that a traceback is the appropriate one?  I'm not sure how one might go about doing this so any tips will be very helpful.
 We discussed this before in #4254 (which is talking about the same issue - but didn't get set up for Travis). Don't really need to have a test case for traceback, because it's not really something you can or should test.
 right...now i remember. ok then
 Ok, in that case how do I force Travis to run since there's nothing new to commit?  Should I delete this pull request/commit and start over?  It looks like Travis is set up OK with my account as far as I can tell.
 ```
git commit --amend -C HEAD
git push origin mybranch -f
```

will reset the commit hash
 Done.  Let me know if you need anything else.  Looks like the build passed.
 @jreback @cpcloud this is good (and worthwhile) to merge. And @cpcloud note that it actually fixes the issue you had to mess with to resolve #4403 :grin:
 @bburan-galenea I know this is trivial, but can you put a release notes mention ? (so we don't forget when this was actually changed)? thanks...then can merge
 Certainly.  Do you mean edit https://github.com/pydata/pandas/blob/master/doc/source/release.rst and add a note under "bug fixes"?
 @bburan-galenea yes, that's correct.
 Ok, I added the note to release.rst and squashed the commits together.
 can you add the original issue in the release notes as well, #4254? which this PR will close
 never mind, that is another PR that looks like a dup of  yours (or maybe yours is a dupe of his!) either way...
 Thanks!
 thank you sir!

keep em coming
