rx-makecall-race-fix-20050518

rx-makecall-race-fix-20050518

On at least one system it was noticed that threads waiting in rx_NewCall
would starve forever (aka deadlock).   This was the result of one out of
two problems related to a race condition on the RX_CONN_MAKECALL_WAITING
bit flag.  This flag was set once in rx_NewCall and cleared in rx_EndCall.
However, it was possible for the flag to be cleared even though there
were additional flags waiting in rx_NewCall.  This was due to a failure
to check the value of makeCallWaiters before clearing the flag and also
due to a failure to properly lock the access to the makeCallWaiters field.

The second problem was an ability to destroy a connection on which threads
are waiting within rx_NewCall.