In an attempt to fix the accounting for dynamic memory allocation
it turned out that coregrind freely allocates memory on the tool
arena (which it should not, conceptually) and tools rely on coregrind
doing so (by VG_(free)'ing memory allocated by coregrind).
Entangling this mess is risky and provides little benefit except
architectural cleanliness. 
Thinking more about it... It isn't really all that interesting how
much memory is allocated by tool code in and by itself.  What is
interesting is the total memory impact a tool has, e.g. as compared
to running "none".
So in this patch the number of memory arenas is consolidated by
subsuming VG_AR_TOOL/ERRORS/EXECCTXT into VG_AR_CORE.
VG_(malloc) and friends have been modified to operate on VG_AR_CORE.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13575 a5019735-40e9-0310-863c-91ae7b9d1cf9