first run of cronjob was never successful

The trap that created cronjob bracktrace archive happen later than the
find performing clean ups, and the find were trapped by ERR with no
such directory.  Second run obviously did work, as the at-exit trap had
ran once.

This commit also fixes variable quoting, so that if a cronjob script
name has a white space in name (generally a bad idea) various file
operations still work.  Hopefully this is a fix to a theoretical issue.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>