Silence error message output generated by libqpol.
Add a lookup function for types/attributes.

Fix SWIG to properly raise exception on error.
Change infoflow to use TypeAttr objects rather than string representations

This will also catch invalid types passed in for analysis.
Fix symbol hashing and provide more useful symbol repr

Hash on the value since there are multiple levels of indirection to the
underlying object.  Otherwise hashing keys never match up multiple
instances of a Python object that point to the same policy object.

Also add a repr function that will make debugging doable when dealing
with Symbol objects instead of string representations.
Throw error in seinfoflow when target is specified but not used.