Request for review (M): 7132070: Use a mach_port_t as the OSThread thread_id rather than pthread_t on BSD/OSX

[Staffan Larsen]

Please review the following change:

Bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7132070

Webrev: http://cr.openjdk.java.net/~sla/7132070/webrev.00/

This changes the value returned by OSThread::thread_id() and 
os::current_thread_id() on macosx to return the mach thread_t instead of 
pthread_t. There is a separate method OSThread:pthread_id() that returns the 
pthread_t. 

The reason for this change is both that JFR would like a 4 byte value for 
thread id, and that SA requires access to the thread_t.

Thanks,
/Staffan