Fix a bug that caused exceptions to be returned, not raised.
Fix a bug that caused exceptions to be returned, not raised.

GraphAPI#_parse currently returns exceptions rather than raising them in
order to not fail batch requests, but for the sake of the rest of the
codebase we should probably try a different approach.

jwjohns/facepy,jgorset/facepy,merwok-forks/facepy,buzzfeed/facepy,Spockuto/facepy,jwjohns/facepy,liorshahverdi/facepy