garu/Clone — pull request #2 by Tux (2013-06-30 16:16:12+00:00)
Title: SV's can be NULL (shit happens) (fixes RT86217)

Though it is not recommendable, and VERY hard to do from a pure-perl
api, it isn't that hard for XS to set SV slots to NULL. In some cases
this can be measurable faster than using PL_sv_undef or similar.