/*
=for apidoc av_shift
-Shifts an SV off the beginning of the
-array. Returns C<&PL_sv_undef> if the
-array is empty.
+Removes one SV from the start of the array, reducing its size by one and
+returning the SV (transferring control of one reference count) to the
+caller. Returns C<&PL_sv_undef> if the array is empty.
Perl equivalent: C<shift(@myarray);>