1.0.46.27: fix mach port leakage

1.0.46.27: fix mach port leakage

 * store mach_thread_self() results in current_mach_thread and
   deallocate the mach_port after thread_set_exception_ports call

 * fix error messages in lose strings in mach_thread_init

 * catch_exception_raise now calls mach_port_deallocate for the
   exception_port, the thread and the task

 * These changes seem to get rid of most of the leaking port
   rights. However, MachPortDump shows when running the
   threads.impure.lisp tests, there are still a number of ports that
   stick around with a single send right.