Hole Punching V3

[Josef Bacik]

This is version 3 of the hole punching series I've been posting.  Not much has
changed, the history is below

V2->V3
-FALLOC_FL_PUNCH_HOLE must also have FALLOC_FL_KEEP_SIZE in order to work
-formatting fixes

V1->V2
-Hole punching doesn't change file size
-Fixed the mode checks in ext4/btrfs/gfs2 so they do what they are supposed to

I've updated my local copies of the xfsprogs patches I have to test this to use
KEEP_SIZE and PUNCH_HOLE together, I'll post them after it looks like these
patches are good to go, including the manpage update.  The xfstest I wrote ran
fine both on xfs and btrfs (failing on btrfs obviously).  Thanks,

Josef