common: Updated postinst to make sure an existing ssl.crt isn't recreated if it is more recent than the key.

This brings them into line with pure-ftpd.

should include the ssl bundle, where appropriate.

Specifically:

The day of a command's execution can be specified by two fields — day of month,
and day of week.   If  both  fields  are restricted (i.e., aren't *), the
command will be run when either field matches the current time.  For example,
``30  4  1,15  * 5'' would cause a command to be run at 4:30 am on the 1st and
15th of each month, plus every Friday.

They now always run in the foreground, and have no forking code
integrated.  Under sysvinit the forking is now managed by
stop-start-daemon.

Also fixed units into powers of 10 (GB) rather than powers of 2 (MiB)