Make Resque.schedule= set, not append

Ensures that any jobs that were previously added to the schedule, but that have since been removed from the config, will be removed from the schedule when the new config is passed to Resque.schedule=.
Don't redirect stdout/stderr when BACKGROUND=true

Ruby 1.9's Process.daemon redirects stderr/stdout to /dev/null
which makes logging impossible. This change prevents
Process.daemon from redirecting stderr and stout to /dev/null
unless ENV['MUTE'] is set.
FIX: avoid using Redis keys command since it scans the whole db keys

Keep track of the timestamps at which a give job occurs in a separate
set. This is redundant but useful if you want to provide a way to remove
scheduled jobs without potentially incurring in seriously performance
issues.
Add a migration script to be used to migrate to
the new job timestamps tracking on an existant
resque-scheduler redis db.
Add scheduled_at method

It returns an array of timestamps the selected job is scheduled at
Merge pull request #1 from potomak/master

Find job schedules time
Delete set tracking timestamps on remove_delayed

When removing all occurencies of a given delayed item remove also the
key used to track the timestamps at which the job was scheduled.
Merge branch 'master' of github.com:bugant/resque-scheduler
Remove items from the timestamps set instead of deleting it

Remove items instead of deleting the timestamp set. This prevent to
delete some new jobs added while deleting the old ones.
Remove elements from the timestamps set in next_item_for_timestamp and remove_delayed_job_from_timestamp
Add test to check that after reset no timestamps set is left
Adding locking to support master fail over
Adding test cases
Merge branch 'master' into locking
updating readme and comments
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