pthreads_fork test is flaky

_From [rnk@google.com](https://code.google.com/u/rnk@google.com/) on October 16, 2012 16:06:11_

Example failing build: http://build.chromium.org/p/client.dynamorio/builders/linux-dr/builds/15 The assert text:
code_api|pthreads.pthreads_fork => Application /mnt/data/b/build/slave/linux-dr/build/build_debug-internal-64/suite/tests/bin/pthreads.pthreads_fork (22215). Internal Error Internal DynamoRIO Error: /mnt/data/b/build/slave/linux-dr/dynamorio/core/heap.c:1331 IF_WINDOWS(doing_detach || ) heapmgt-vmheap.num_free_blocks == heapmgt-vmheap.num_blocks - perstack \* 1 - perstack \* ((IF_WINDOWS_ELSE(doing_detach, false) IF_APP_EXPORTS(|| dr_api_exit)) ? 0 : 1)

What it means is that we leaked something during shutdown, which is much better than the deadlock we used to get for issue #239 . If we manage to sync before the fork, in theory we can reset in the child and avoid memory leaks, but apparently it's not bulletproof.

See issue #239 and r1382 which tried to fix it.

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=951_