Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Sync with OpenBSD's dirname(3) - license change, avoid strcpy() over
string constant, use memcpy() instead of strncpy() and improve code
readibility. No functional change.

Fix LP64 architectures and especially ia64. Functions that return
a pointer and lack a prototype will have the return value (assumed
to be an integer) zero-extended to a pointer. On ia64 this is
unconditionally fatal as it zeroes-out the region bits, forming an
invalid pointer. Fix the sigsegv by including <stdlib.h>.

Pointy hat: bbraun

Reduce libc.so's memory footprint by lazily allocating memory used internally
by basename() and dirname().
Reviewed by: eric

* Remove 'register'. (some functions had 7+ register functions...)
* Fix SCM ID's.

Fixed world breakage due to missing include of <sys/cdefs.h> in previous
commit.

Fixed related style bugs:
basename.c: misplaced '#if 0'
dirname.c: misplaced '#if 0'
getgrent.c: missing '#if 0', and tab lossage in vendor id (the previous
commit fixed the complete corruption of the vendor id but
lost a tab)
getpwent.c: missing '#if 0'

Fix FreeBSD IDs.

Fix a one-byte overrun.

PR: 28472
Submitted by: David Xu <davidx@viasoft.com.cn>
Obtained from: OpenBSD

Import XPG4-compliant basename(3) and dirname(3) from OpenBSD.
The man pages need some adjustments.

PR: 12960, 12962
Submitted by: James Howard <howardjp@wam.umd.edu>
Obtained from: OpenBSD