add event for app code modification or for code region being flushed

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on March 08, 2011 10:13:46_

for clients to update data tied to application code, the module unload
event covers the most common cases, but for other code changes the
fragment_delete event is not usable enough. it only passes the tag, it's
not always safe to decode forward in a no-longer-read-only region, and
clients don't necessarily know where the fragment ends, especially if a
trace.

DR should raise a new event on each whole region being flushed, for every
flush, regardless of the source of the flush, since code anywhere in the
region could change after removal from executable_areas (if writable,
anyway, but could be made writable later).

this would help solve these Dr. Memory issues:
issue #260: remove xl8_sharing_table and ignore_unaddr_table entries on code mod
issue #114: remove post_call_table and call_site_table entries on code mod

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=409_