perldiag: remove space from otherwise blank line

This enables splain to find the following entry.
Alphabetise perldiag
perldiag: ‘my sub’ is no longer ‘reserved’ syntax
Unwrap a perldiag entry for better splain output

Before:

$ ./perl -Ilib -Mdiagnostics -e 'warn "Missing '\'']'\'' in prototype for %s : %s"'
Missing ']' in prototype for %s : %s at -e line 1 (#1)
    (W illegalproto) A grouping was started with [ but never closed with
    ].

After:

$ ./perl -Ilib -Mdiagnostics -e 'warn "Missing '\'']'\'' in prototype for %s : %s"'
Missing ']' in prototype for %s : %s at -e line 1 (#1)
    (W illegalproto) A grouping was started with [ but never closed with ].
gv.c: Remove redundant mro_method_changed_in()

Core subs are already accounted for by method lookup, so vivifying
them does not change what gets inherited.  Hence, there is no need
to flush caches here.
Fix memory leak with recursive sub redefinition

See the thread starting at
<20131115042923.7514.qmail@lists-nntp.develooper.com>.

Commits 7004ee4937 and a61818571 changed subroutine redefinition to
null the GvCV slot before freeing the CV, so that destructors won’t
see GvCV without a reference count.  That turns a double free into a
memory leak.

Kent Fredric explains it nice and clearly:

> sub foo{}   # A
> bless \&foo;
> DESTROY { *foo = sub {}  # C }
> eval "sub foo{} "; # B
>
> Previous behaviour was:
>
> B replaces A, triggers DESTROY, which triggers C replacing A, and this
> invoked a double free, because C , triggering the removal of A,
> happened while A still existed ( ?? )
>
> So the change fixes this, so that A is removed from the symbol table
> before DESTROY triggers , so that C is creating a "new" symbol,
> effectively, and the problem is that C is then clobbered by the B
> replacing the slot, after the DESTROY.

So C leaks.

This commit fixes it by changing the SvREFCNT_dec into SAVEFREESV,
essentially delaying the DESTROY until after the subroutine redefini-
tion is complete.

This does mean that C is what ends up in the glob afterwards; but as
long as perl’s own bookkeeping is thrown off, we can leave it to the
user (the Perl programmer) to handle the consequences of naughty
destructors.
perldelta for the previous commit