Correct the page count when excess length is trimmed from the bio.

Reported and tested by:	Ivan Klymenko <fidaj@ukr.net
- Make 'flags' argument to chflags(2), fchflags(2) and lchflags(2) of type
  u_long. Before this change it was of type int for syscalls, but prototypes
  in sys/stat.h and documentation for chflags(2) and fchflags(2) (but not
  for lchflags(2)) stated that it was u_long. Now some related functions
  use u_long type for flags (strtofflags(3), fflagstostr(3)).
- Make path argument of type 'const char *' for consistency.

Discussed on:	arch
Sponsored by:	The FreeBSD Foundation
Regenerate after r248597.

Sponsored by:	The FreeBSD Foundation
Implement chflagsat(2) system call, similar to fchmodat(2), but operates on
file flags.

Reviewed by:	kib, jilles
Sponsored by:	The FreeBSD Foundation
Regenerate after r248599.

Sponsored by:	The FreeBSD Foundation
Document chflagsat(2).

Obtained from:	jilles
Fix for building libzpool under i386.

Reviewed by:	pjd (mentor)
Approved by:	pjd (mentor)
MFC after:	2 weeks
Update regression tests after adding chflagsat(2).

Sponsored by:	The FreeBSD Foundation