better support for adaptive instrumentation: add callback to synch flush

_From [zhao...@google.com](https://code.google.com/u/106321947286816917100/) on May 10, 2012 13:48:20_

DynamoRIO tries to support adaptive instrumentation, i.e. changing the instrumentation during the execution.
However in a situation of a fault event, the client may have trouble to reconstruct the instruction list because it does not know which version of instrumentation should be performed.

One possible solution is to let client maintain a per-bb data structure to keep track of which version of instrumentation it performed on the bb, and retrieve it on every reconstruction/translation.

For simple situation like flush whole code cache and re-instrument every code fragment, a synchronized flush with callback to update might work.

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=772_