xrddefault: Use parsed and massaged main temp_file for retention data

Changing things around so config parsing happens in *one* place
would've been a pretty good idea quite some time ago, but this
will at least make retention data temp-files go to the right
place.

Signed-off-by: Andreas Ericsson <ae@op5.se>
core: Refuse to start if modules don't load for some reason

Since nebmodules are an integral part of the Nagios system the
user expects to bring to life (as of several years now), failure
to load one or more of them should be considered critical.

Suggested-by: Mark Frost <mark.frost1@pepsico.com>
Signed-off-by: Andreas Ericsson <ae@op5.se>