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)

Update prototype for function pmap_init(), it no longer has the arguments
phys_start and phys_end.

Remove a stale documentation not about dis/uncontiguous memory.

Update manual page date while I am around these ends.

Reviewed by: alc

Fixed the .Os call (missing or wrong).

Add manual page documentation for the machine-independent PMAP subsystem.
Include documentation of alc's new pmap_extract_and_hold() function.

Reviewed by: hmp
Approved by: jake (mentor)