* thread.cc (pthread_mutex::pthread_mutex): Change default type
	to PTHREAD_MUTEX_NORMAL.
	(pthread_mutex::unlock): Return EPERM if the mutex has no owner and
	the mutex type is PTHREAD_MUTEX_ERRORCHECK, as on Linux.
	(pthread_mutexattr::pthread_mutexattr): Ditto.
	(pthread_mutex_unlock): Do not fail if mutex is a normal mutex
	initializer.
	* include/pthread.h (PTHREAD_MUTEX_INITIALIZER): Redefine as
	PTHREAD_NORMAL_MUTEX_INITIALIZER_NP.
	* thread.cc (pthread_mutex::pthread_mutex): Change default type
	to PTHREAD_MUTEX_NORMAL.
	(pthread_mutex::unlock): Return EPERM if the mutex has no owner and
	the mutex type is PTHREAD_MUTEX_ERRORCHECK, as on Linux.
	(pthread_mutexattr::pthread_mutexattr): Ditto.
	(pthread_mutex_unlock): Do not fail if mutex is a normal mutex
	initializer.
	* include/pthread.h (PTHREAD_MUTEX_INITIALIZER): Redefine as
	PTHREAD_NORMAL_MUTEX_INITIALIZER_NP.
	* uinfo.cc (cygheap_domain_info::init): Correctly set
	lowest_tdo_posix_offset to UNIX_POSIX_OFFSET.
	(fetch_posix_offset): Redesign to fake a POSIX offset in all cases
	where we can't fetch a non-0 POSIX offset from our primary domain.
	* uinfo.cc (cygheap_domain_info::init): Correctly set
	lowest_tdo_posix_offset to UNIX_POSIX_OFFSET.
	(fetch_posix_offset): Redesign to fake a POSIX offset in all cases
	where we can't fetch a non-0 POSIX offset from our primary domain.
	* libc/include/sys/errno.h: Fix comments.
	* libc/string/strerror.c: Fix documentation.
	(_strerror_r): Handle ENETRESET, EILSEQ, ENODATA, ECONNRESET,
	EADDRNOTAVAIL, EOVERFLOW.  Fix strings for EMFILE and EDOM.
	* libc/include/sys/errno.h: Fix comments.
	* libc/string/strerror.c: Fix documentation.
	(_strerror_r): Handle ENETRESET, EILSEQ, ENODATA, ECONNRESET,
	EADDRNOTAVAIL, EOVERFLOW.  Fix strings for EMFILE and EDOM.
* sigproc.cc (send_sig): Fix bad format in diagnostic output.
* sigproc.cc (send_sig): Fix bad format in diagnostic output.