put malloc replace code into app library and support loading up front pre-attach

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on June 13, 2012 14:50:51_

in the end similar to current replace_malloc, though does make handling the
lock API simpler (but not fundamentally different: identical to shifting
the heap lock to still be in the code cache)

but, needs to be an app library for pattern attach: want to set redzone
size and pattern fill up front even before attach. want to share error
reporting code pre-attach (invalid free, e.g.) with pattern errors
post-attach.

API callbacks to tool best implemented as annotations => need DRi#283
annotation framework

app library would use standard namespace replace on linux and hooks (whether direct or IAT) to replace on windows

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=910_