Fix bug where scheduler sleeps when processing a delayed queue

[mhagstrand]

The function handleDelayedItems() was overwriting the parameter
$timestamp from the call nextDelayedTimestamp() with timestamp of
the most delayed job. Therefor it would only process 1 seconds
worth of items before sleeping. A slighty delayed queue could
fall very far behind.

[rolfvreijdenberger]

duplicate of #33
I think it's wise to review both this patch (which keeps the $timestamp parameter as input for the method) and #33 which does not keep it (seems to be not needed in the called method itself).
In case of the same functionality, I'd prefer the simplest (#33) but then we would also need to change the called method ResqueScheduler::nextDelayedTimestamp($timestamp) to not use $timestamp.

@chrisboulton can you update me on this, I'd be more than happy to get alter the code appropiately
@danhunsaker @chrisboulton will this repository also be maintained by a group of people?

[chrisboulton]

I think I actually prefer the fix here vs in #33. #33 doesn't respect whatever timestamp was passed, which I know while isn't used today, is somewhat of a breaking compatibility change.

[rolfvreijdenberger]

fair enough. thanks for merging a fix.
the discussion over removal of dead code can be done elsewhere 👍