The C compiler will pick an enumeration type that accomodates the specified
values for the enumeration, so ignoring 64-bit enumerations, we can
have enumeration values from MININT32 to MAXUINT32. To handle this properly:
- Use gint64 for holding eumeration values when scanning
- Add a 'unsigned_value' bit to ValueBlob so we can distinguish the
int32 vs. uint32 cases in the typelib
- Change the return value of g_value_info_get_value() to gint64.
https://bugzilla.gnome.org/show_bug.cgi?id=629704
