better Mac thread support: earlier ptrhead interception, and intercept workqueue threads and raw Mach threads

From bruen...@google.com on March 27, 2014 16:47:57

For initial thread support to get simple pthreads apps working I'm just planning to intercept bsdthread_create(). This intercepts threads a little late, and misses workqueue threads. But we need earlier injection in order to intercept bsdthread_register() and intercept the entries for both regular and workqueue threads.

We also want to eventually handle raw Mach threads created via other means.

Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1403