Throw away tmp files if mv fails

Attempt to get rid of stale temp files that occasionally drop. While
there is anecdotal evidence that this doesn't solve the problem, it
doesn't hurt, and it's the only place I can see to fix it.
revert warning if z.sh is being exec'd and not sourced

Because we can't reliably determine if we're really being exec'd.
Merge branch 'master' into dev