* fork.cc (fork_parent): Save parent pid in a temporary variable since child

* fork.cc (fork_parent): Save parent pid in a temporary variable since child
could conceivably exit before function returns, rendering the child's shared
memory area invalid.
* cygtls.h (_cygtls::incyg): Declare new field.
(_cygtls::in_exception): Define new function.
* exceptions.cc (setup_handler): Remove locked flag.  Use 'incyg' flag and
in_exception function to determine when we're in a cygwin function.
(_cygtls::call_signal_handler): Decrement incyg flag prior to calling a
handler.  Increment it on return.
* gendef (_sigfe): Increment incyg flag.  Use testl for zero testing rather
than orl, for consistency.
(_sigbe): Decrement incyg flag.  Use testl for zero testing rather than orl,
for consistency.
(_cygtls::pop): Use testl for zero testing rather than orl, for consistency.
(stabilize_sig_stack): Ditto.