LinuxServer Changes:
Install unrar from linuxserver repo.
mylar3 Changes:
rsscheck: undo erroneous changes to nzbdbsearch's return type
In dab1bf372fba803c58516bd78d1ef94e721bd42b I simplified the return
types of functions whose return values are passed to
search_check.checker. nzbdbsearch's return value is used in a
different way, and so I should never have changed it. Apologies!
Fixes: #1403