[perl #111610] Trouble with XS-APItest/t/clone-with-stack.t

I ran into a bit of a problem when building perl-5.16.0.
'make test' showed a segfault in ext/XS-APItest/t/clone-with-stack.t.
It seems to be caused by accessing already freed memory, it
segfaults because I have MALLOC_PERTUBE_ set, thus glibc fills
freed memory with some value.

Digging deeper, it seems like perl_clone() does not fix
the cx's blk_oldcop element when doing context cloning, thus
blk_oldcop still points to PL_compiling in the old interp--the
calling scope for the BEGIN block being the compilation of the
code surrounding it--and the POPBLOCK done in leavesub will copy
the data from the old interp to PL_curcop.

After fixing this, it still crashed because interp_dup->Iop was
zero after the runops_standard() call (which is probably
correct as the end of the BEGIN block was reached). So I
also added an if statement that checks the pointer.
bump XS-APItest version
bump version to 5.16.3
perldelta for 5.16.3
note that we are building 5.16.3-RC1
Encode: Fixed a memory leak that occurred in the UTF-8 encoding.

The decode and encode methods allocated a SV for the result, this SV
is passed to the process_utf8() function which may croak() if the
CHECK flag has FB_CROAK set.
bump version number of Encode by _01
add 5.16.3 to Module:Corelist
perldelta: Module::CoreList update
perldelta: Encode update
perlhist: date for 5.16.3-RC1
update Module::CoreList for non-RC release
final changes for release as 5.16.3