* cygmalloc.h: Make more concessions to attempts to get debugging malloc
working.
* debug.h: Ditto.
* dlmalloc.cc: Ditto.
* dlmalloc.h: Ditto.
* malloc_wrapper.cc: Ditto.
* perthread.h (perthread::create): Use calloc to ensure zeroed memory.
* sigproc.h (sigCONT): Declare.
(wait_sig): Create sigCONT event here.
* exceptions.cc (sig_handle_tty_stop): Wait for sigCONT event rather than
stopping thread.
(sig_handle): Set sigCONT event as appropriate on SIGCONT rather than calling
ResumeThread.