- Don't update checksum or last_checked when a path matches one
   already in the db. This isn't quite right, will be fixed in next
   commit.
 - Don't assume all non-crawler sections are plugins. Rather identify
   plugin sections by the 'plugins' option in the 'crawler' section.
 - Don't delete test files if -k option is on the command line.
 - Only reset last_check and checksum if the item type changes
Working on Alert class and tests for it