[PATCH] Don't use GvCV() as an lvalue, that broke with Perl 5.13.10 As seen in [rt.cpan.org #64987], GvCV() can't be assigned to anymore so use the new GvCV_set() macro when available or implement it the old way if it isn't.
Also, set up a SAVEDESTRUCTOR function to restore the old CV value because we can't store it in the GV anymore. This part was adapted from Scope-Upper-0.14 by Vincent Pit.
