Add a preflight check for ~/.wgetrc

ownCloud moved their source code to a new location, breaking our installation script.

Fixes #741.

Create a temporary multiprocessing pool

Add check to preflight for exec on tmp

Allow files in /home/user-data/mail/mailboxes

(re-fix) mail sent from an address on a subdomain of a domain hosted by the box (a non-zone domain) would never be DKIM-signed because only zones were included in the openDKIM configuration, mistakenly

This was originally fixed in 143bbf37 (February 16, 2015). Then I broke it in 7a93d219 (November 2015) while doing some refactoring ahead of v0.15.

Reduce percentages for required free memory checks

When previous panel was login, move to system_status

Reduce number of processes in the pool to 5

Fix small typo in comments

the logic in 4ed23f44 for taking backups more often was partly backward

This reverts commit b32cb622.

Fixes #627. Fixes #653. Closes #714.