Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Hide the implementation details about multiple threading libraries
from the synopses of pthread*(3) manpages.

Reviewed by: deischen, davidxu

Removed the IMPLEMENTATION NOTES section made redundant by not
putting libc_r into the LIBRARY section.

Document interfaces that are supported by libthr.

Spell POSIX threads library as "libpthread", mdoc(7) is smart
enough to render it as "-lkse" these days.

This interface is not provided by libc_r. It is, on the other
hand, is also provided by libthr, but this will be addressed
later.

Aargh, cvs add pthread_mutex_timedlock