free pre-us allocs and heaps for -replace_malloc

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on April 25, 2013 22:04:29_

pre-us allocs are currently leaked. normally there are at most a few hundred.
but for attach this is not an acceptable solution.

call native free? but if replacing many layers can we call RtlFree in
place of any of them? need to record which layer they're in (want to do
that for issue #607 A too).

**\* TODO attach or late injection: HeapDestroy on heap w/ mixtures of pre-us and post-us allocs!

for a Heap that exists before we take over, we'll need to invoke the real
RtlDestroyHeap

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=1195_