* cygheap.cc (cfree): Remove malloc debugging probe.

* cygheap.cc (cfree): Remove malloc debugging probe.
* dlmalloc.c (errprint): Remove abort() call which causes interesting error
message printing to abort prematurely.
* environ.cc: Sprinkle MALLOC_CHECKs liberally throughout.
(_addenv): Allocate two empty elements at end of environ to
(apparently) work around problems with some buggy applications.
(winenv): Avoid calling alloca if no forced environment variable is present.

* exceptions.cc (open_stackdumpfile): Don't print "Dumping stack trace to..."
when running in a cygwin environment (i.e., the parent is a cygwin process).

* dtable.cc (dtable::init_std_file_from_handle): Move device type detection
code from build_fhandler here since it is only used by this function.
(dtable::build_fhandler_from_name): New method.  Renamed from
dtable::build_fhandler.
(dtable::build_fhandler): Use build_fhandler_from_name.
(cygwin_attach_handle_to_fd): Ditto.
* syscalls.cc (_open): Ditto.
(stat_worker): Ditto.
* dtable.h (dtable::build_fhandler_from_name): Rename declaration from
dtable::build_fhandler.