fetcher: refactored the fetch loop to be smaller
fetcher: if signaled to quit, unclaim immediately
README: added walker-user mailing list
dispatcher: do not dispatched when excluded=true

Added the excluded and excluded_reason columns to walker.domain_info.
Expecting that we'll have the console make use of those soon, but at
least with this it works if we set excluded manually.
Merge pull request #57 from iParadigms/fetch-manager-fast-shutdown

Fetch manager fast shutdown
Merge pull request #58 from iParadigms/readme-mailing-list

README: added walker-user mailing list
Merge pull request #59 from iParadigms/dispatcher-exclude

dispatcher: do not dispatched when excluded=true
Merge branch 'master' into NewCrawlTags

Conflicts:
	fetcher.go
	test/fetcher_test.go