* cygthread.cc (cygthread::initialized): Avoid copying on fork or some threads

* cygthread.cc (cygthread::initialized): Avoid copying on fork or some threads
may not end up in the pool.
(cygthread::new): Avoid race when checking for initialized.  Add debugging
code.
* fhandler.cc (fhandler_base::raw_read): Add case for ERROR_INVALID_HANDLE due
to Win95 directories.
(fhandler_base::open): Handle errors due to Win95 directories.
(fhandler_base::close): Add get_nohandle () test.
(fhandler_base::set_close_on_exec): Ditto.
(fhandler_base::fork_fixup): Ditto.
(fhandler_base::lock): Change error code to Posix EINVAL.
(fhandler_base::dup): If get_nohandle (), set new value to INVALID_HANDLE_VALUE
instead of NULL.
* fhandler_disk_file.cc (fhandler_disk_file::fstat): Call fstat_by_name if
get_nohandle ().  Remove extraneous element from strpbrk.
(fhandler_disk_file::open): Remove test for Win95 directory.
* fhandler_random.cc (fhandler_dev_random::open): Add set_nohandle ().
* fhandler_clipboard.cc (fhandler_dev_clipboard::open): Ditto.
* fhandler_zero.cc (fhandler_dev_zero::open): Ditto.
(fhandler_dev_zero::close): Delete.
* fhandler.h (class fhandler_dev_zero): Ditto.