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

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

MFC: 228545,229572

Modify pw_copy:
- if pw is NULL and oldpw is not NULL then the oldpw is deleted
- if pw->pw_name != oldpw->pw_name but pw->pw_uid == oldpw->pw_uid
then it renames the user

add new gr_* functions so now gr_util API is similar to pw_util API,
this allow to manipulate groups in a safe way.

Add new pw_make_v7 to make a passwd line (in v7 format) out of a struct passwd

Approved by: des (mentor)

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

Approved by: re (implicit)

Remove a dead store.

MFC after: 5 days

Fixed style issues with variable ordering and naming, spacing and
parentheses.

Fixed alignment issue in gr_dup() in its assignment of gr_mem using a
struct to force alignment without performing alignment mathematics. This
was noticed recently with libutil was built with WARNS=6 on platform such
as sparc64.

Added checks to gr_dup(), gr_equal() and gr_make() to prevent segfaults
when examining struct group's with the struct members pointing to NULL's.

With fix of alignment issue, restore WARNS?=6.

Reviewed by: des
MFC after: 1 week

style(9) fixes.

MFC after: 1 week

Add four utility functions related to struct grp processing modeled in-part
after similar calls related to struct pwd in libutil/pw_util.c:
- gr_equal()
Perform a deep comparison of two struct grp's. It does a thorough, yet
unoptimized comparison of all the members regardless of order.

- gr_make()
Create a string (see group(5)) from a struct grp.

- gr_dup()
Duplicate a struct grp. Returns a value that is a single contiguous
block of memory.

- gr_scan()
Create a struct grp from a string (as produced by gr_make()).

MFC after: 3 weeks