Hopefully this fixes http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=656968#31
and future incarnations of this class of bugs.

Using 'warning' and 'return' instead of a fatal at rotate_long if
backuproot doesn't exist. Using a warning ensures that the backup
action can process the other includes and not just exit.

Quoting $exclude and $excludes and avoiding a for loop on $exclude to not expand wildcards in beforehand (upstream #3882)