Providing array for warning/critical messages

Messages can be pushed to the apropriate @warning_msgs or @critical_msgs array.

OK/Warning/Critical state is set depending on the number of messages in the @warning_msgs and @critical_msgs arrays.
Put all warning/critical messages in one line

Replaced newline (\n) by a comma (,).
Add check of pacman's repository files

Sample output:
WARNING: No packages need updating. Oldest DB file is /var/lib/pacman/sync/extra.db. | packages=0
Warning messages: File '/var/lib/pacman/sync/extra.db' is too old, File '/var/lib/pacman/sync/community.db' is too old, File '/var/lib/pacman/sync/core.db' is too old.