Change the Mutex::Locker class so that it takes the Mutex object and locks it, rather

than being given the pthread_mutex_t from the Mutex and locks that.  That allows us to
track ownership of the Mutex better.  

Used this to switch the LLDB_CONFIGURATION_DEBUG enabled assert when we can't get the
gdb-remote sequence mutex to assert when the thread that had the mutex releases it.  This
is generally more useful information than saying just who failed to get it (since the
code that had it locked often had released it by the time the assert fired.)

llvm-svn: 158240