Update the backup creation code so that the largest numbered file
is always the most recent backup. Also the number of backups is now
exposed as a preference with 1 as the default.
make backup by default
OK, go back to foo.sfd~1 being the most recent, but make sure that
foo.sfd is the very latest (just saved file).
Merge pull request #310 from monkeyiq/2013feb/backupsreorder

2013feb/backupsreorder