updated tox with slightly better syntax
updated MANIFEST.in to preserve pxd files
implemented contextTime -- see #4
implemented processContextToken -- see #4
implemented importSecContext and exportSecContext -- see #4
updated readme requirements to reflect landing of cython refactor
added implementation and tests for acquireCredImpersonateName -- see #31
added some things to type_wrappers to facilitate the s4u class development
fixed some bugs in type_wrappers.py
s4u support working...
fixed up some of the type wrapper code (it really needs tests, added a 'not None' statement to acquireCredImpersonateName's impersonator_cred argument
s4u support working -- helper class in place, fixes to type wrappers to facilitate