add a post-instru pass that checks for errors in register preservation

_From [derek.br...@gmail.com](https://code.google.com/u/117968039472581148324/) on December 10, 2010 17:58:09_

PR 494720

implementing fastpath improvements is getting more painful as more
complexity is added. more automatic debugging checks are needed. this
case covers implementing a post-instru pass that ensures app register
values and cross-instr shared translations are preserved properly.
it may require annotations added during instru add time (note that
we can't do reg checks then since not added in order).

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=164_