documented workaround for frameworks that extend optional libraries
Use UIImagePNGRepresentation to preserve transparency
Only perform `NSLog` statements if `SD_VERBOSE` is defined
Merge pull request #551 from robertmryan/master

SDWebImagePrefetcher should only perform `NSLog` statements if `SD_VERBOSE` is defined
Merge pull request #552 from garnett/master

Use UIImagePNGRepresentation to preserve transparency (fix for #545)
Added SDWebImageOption to enable Cookies Handling.
Merge pull request #553 from danpe/master

Added SDWebImageOption to enable Cookies Handling.
Allow setting a custom memory cost limit for the in-memory NSCache. This can help to keep memory down before memory warnings are sent by the device.
NSInteger -> NSUInteger, add getter method
Merge pull request #556 from JoshuaGross/master

Allow setting a custom memory cost limit for the in-memory NSCache.
up version 3.5 in podspec to be consistent with latest
Merge pull request #558 from shifu/master

up version 3.5 in podspec to be consistent with latest
Add HTTP header filter to pick headers for downloading request
Merge pull request #514 from crazytonyli/header-picking

Add HTTP header passing test to pick header for downloading request
added currentDownload Count, to allow someone to see how many operations are left.
matched coding conventions
Merge pull request #562 from mknippen/master

added currentDownload Count, to allow someone to see how many operations are left.
Bump version to 3.5.1 (fix #568)
Added a delegate for the web image prefetched.
Code cleanup.