track alloc counts per callstack for leak diagnosis

_From [derek.br...@gmail.com](https://code.google.com/u/117968039472581148324/) on December 10, 2010 17:58:15_

PR 514043

for analyzing leaks, reporting the count of allocations from that callstack
and the ordinals of the ones that leaked would be useful

then you'd know "ok it's the 53rd instance here that leaked, so it's on
some rare path, and from the timetamp (PR 465163) it happened late in the
run"

this case includes adding the timestamp to leaks that was added to other errors in
PR 465163. we'll have to add it to all stored callstacks which will occupy
some space, so we may want it under a runtime option

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=173_