Updates progress callback to use NSInteger

Pull Request #606 resolves this issue in the code but not in the Documentation.
Merge pull request #685 from jeffleeismyhero/patch-1

Updates progress callback to use NSInteger
Port Max's crash fix to my 3.6 fork
Merge pull request #694 from shifu/master

Port Max's crash fix to my 3.6 fork
Update SDWebImageDownloaderOperation.m

Fixing race condition that causes cancellation of one download operation to stop a run loop that is now used for another download operation. Race is introduced through -performSelector:onThread:withObject:waitUntilDone:
Merge pull request #698 from salling/master

Fixing race in SDWebImageDownloaderOperation leading to erroneous timeout.
Save image in cache before calling completion block
Merge pull request #700 from herrernst/master

Save image in cache before calling completion block
Merge pull request #2 from rs/master

Merge from RS:Master