allow sentinel translation addresses

_From [derek.br...@gmail.com](https://code.google.com/u/117968039472581148324/) on August 04, 2009 12:41:50_

this was PR 307384

xref PR 214962

We'd like to allow the use of sentinel addresses as instr translations, so
the client can use those to index into a table to restore state.
I set up the restore_state option to be called even for only checking
for a safe spot pc, so it is possible on that side.
However, I put in asserts that all translations stay within bb bounds
(including bb components of traces) b/c I was worried about cache
consistency. Also, mangle_trace() from PR 299808 relies on translations
staying within bounds.

This case covers coming up with alternative bb boundary locating for
mangle_trace() and adding a way for advanced users to use sentinels (by
assuring us that they aren't changing app sources, so our cache consistency
will still work).

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=188_