ASSERT (linux/os.c:3049 res == 0) on mprotect +rwx of invalid memory

_From [derek.br...@gmail.com](https://code.google.com/u/117968039472581148324/) on October 12, 2010 15:04:11_

DR's SYS_mprotect handling is not very robust: it doesn't properly undo all failing calls, and for +rwx calls that say extend beyond the valid range it ends up trying to make that region unwritable and hits the assert here.
just about any test case of failing mprotect hits some assert or curiosity. this issue covers cleaning the code up.

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=351_