Fix crash in error handling when creating struct with mismatched info type

Error handling code was attempting to get the PyType of a pointer to a
pointer. Use the correct amount of indirection so an exception is raised as
intended rather than a segfault.
Support union creation with PyGIStruct

Add additional case for allowing the creation bare unions wrapped with
PyGIStruct. This is needed because PyGIStruct wraps both GIStruct and
GIUnion types.
python.m4: g/c JD_PYTHON_CHECK_VERSION

We currently require automake 1.11.1, and its AM_PYTHON_CHECK_VERSION
is identical (made here).

https://bugzilla.gnome.org/show_bug.cgi?id=721662