Refactor pyg_value_from_pyobject into two functions

Break pyg_value_from_pyobject into two functions. One which keeps
Python exceptions queued (pyg_value_from_pyobject_with_error) and
one which clears them (pyg_value_from_pyobject). This allows for
re-use for code which want to keep the errors around

https://bugzilla.gnome.org/show_bug.cgi?id=688081