handle exception in alloc routine: adjust state on unwind

_From [derek.br...@gmail.com](https://code.google.com/u/117968039472581148324/) on December 10, 2010 17:57:48_

PR 408545

if app hits an exception (SEH on Windows or signal on Linux) in heap routine => need to
adjust pt->calling_alloc and pt->in_heap_routine: but difficult to do since need to know what
exception continuation target is

ditto for longjmp

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=120_