TAKE - Merge more Irix mkfs changes

[Eric Sandeen <sandeen@sgi.com>]

     The last change to mkfs missed adjusting the ag count if the last AG
     is too small to be an AG.
     Catch xfs_mount returning NULL (an error) and don't attempt to use
     that mount pointer.

(The second change was actually already in Linux, I tweaked it in this
merge to more closely match the new Irix code).

Date:  Wed May 22 08:55:10 PDT 2002
Workarea:  stout.americas.sgi.com:/localhome/src/sandeen/xfs-cmds/workarea
Inspected by:  sandeen@sgi.com
Author:  overby
Merged by:  sandeen
Merged mods:  irix6.5f:irix:119783a

The following file(s) were checked into:
  bonnie.engr.sgi.com:/isms/slinx/xfs-cmds


Modid:  xfs-cmds:slinx:119783a
xfsprogs/mkfs/xfs_mkfs.c - 1.25