In _pygi_g_type_info_check_object, numbers were checked against the object
which had to implement the number protocol. Although such an object may be
correct, the check required the comparison functions to be implemented in that
object too.

The right way to check those objects is to check the converted
number (an int, long or float) for the bounds, not the original object.

Make the introspection module depend on Python 2.5.2, GLib 2.21.5 (future 2.22)
and GObject-Introspection 0.6.4

This reverts commit fd35a7ae.

When allocations are done by the slice allocator, we need the size to
deallocate, and, in this case, it'd make the release function more complicated.

Normally, introspected boxed types are registered. They might not have been
registered yet, though.

Looking up the type in the repository is now useless, since
pygobject_lookup_class does it if it's not registered yet.