Deparse local our LIST

The ‘local’ was being omitted.  I missed the list form of
‘local our’ in commit f351564117.
op.c:allocmy: Don’t depend on null termination

This function has a len argument, but still depends on its argument’s
being null-terminated in one spot.  (All other parts of the function
use the length.)
op.c:allocmy: Remove obsolete cmnts and assert

We are no longer depending on strlen at all.  The name[2] check was
removed in 2009 in d6447115b.
toke.c:S_parse_opt_lexvar: Don’t use null terminator

allocmy no longer depends on it.
Deparse split-to-our-array correctly

$ ./perl -Ilib -MO=Deparse -e 'our @x = split //, $a'
@x = split(//, $a, 0);

The ‘our’ disappears because ‘split’ swallows up the assignment and
writes to @x directly.  But the result is that no OUR_INTRO flag is
left in the op tree.

Fixing this based on the current op tree is very complicated.  So
this commit sets the flag on the split op and makes B::Deparse
look for it.