Document isgreater(3) and friends.
<sys/proc.h>: Remove suser() and suser_cred() prototypes.

suser_*() was replaced with priv_*() more than 4 years ago.

Reported-by: Joris Giovannangeli <joris@giovannangeli.fr>
taskqueue.9: Use .Er for errors numbers.
kernel: Stop installing pst(4) module and manual page on x86_64.

It is i386 only.
Fix typo in MLINKS line for taskqueue_drain_timeout(9).
strchr.3: Fix typo, it's strchrnul, not strrchrnul.
libm: Fix a typo in the MLINKS line for log2l(3).