Close file handle when nodepath arg to ctable.fromhdf5 is incorrect.

Close the tables file before re-raising the exception that occurs during
node retrieval to prevent leaking file handles.

Catch all exceptions so that NoSuchNodeErrors, ValueErrors and other
errors are all handled.
Merge pull request #40 from quantopian/close-file-on-no-node

Close file handle when nodepath arg to ctable.fromhdf5 is incorrect.