Downstream bug: 
https://bugzilla.redhat.com/show_bug.cgi?id=556200

Description of problem:
Calling vt.get_text and passing True for do_attrs causes a segfault, because
the cht variable in build_attributes is never initialized.

Attached is a patch which fixes the bug, and also these other bugs & warnings:

1. Refcounting in call_callback is incorrect; do not decref the callback
function until after it's called.
2. Eliminate signed/unsigned warning in build_attributes; use guint instead of
int.
3. Remove unused count variables from get_text and related functions.  These
were leftover from when the attribute code was duplicated in each.
4. match_check returns a string and an int, but the local variable was declared
as int*.  Change int* tag to int tag.
5. get_text and related methods are written to support callback=NULL, however
the call to PyArg_ParseTupleAndKeywords makes it a required parameter.  Changed
instances of O|OO to |OOO.

Downstream bug has patch.