ntdll: implement FLG_HEAP_ENABLE_TAIL_CHECK

[Dan Kegel]

On Wed, Nov 18, 2009 at 2:28 PM, Dan Kegel <dank at kegel.com> wrote:
> Here's a second try, this time only for large arenas, but
> with valgrind integration working.  (It also has a workaround for
> a strange valgrind problem that leaves an empty variable in
> the environment that confuses wine.)

Found buglets already, so don't bother doing detailed review...