Using the source image's the color space for image decoding (fix #237)

Should fix most system warnings regarding invalid context configurations
Send out progress callbacks sooner.

- as soon as the NSURLConnection gets initialized
- helps to allocate and show progress indication sooner and prevent large delays without progress indication (for example when the server takes long to respond)
- estimated size is always 0 at this point, clients can use this to decide if they want to handle this callback or skip it
Changed the expected size to -1 in the initial progress callback.

- simplifies callback code by removing possible division by 0 issues during progress computation
Using spaces instead of tabs for indentation.

- also configured the Xcode project to use spaces instead of tabs by default
Merge pull request #249 from matej/early-progress-callback

Early progress callback
Fixed bug where decodedImageWithImage: ignored image scale and orientation.
Merge pull request #252 from reidmain/master

decodedImageWithImage: ignores scale and orientation
Fix an LLVM warning (fix #254)
Fix Xcode 4.6 warnings
isRunning method added at SDWebImageManager
Change SDWebImageManager to use shared image cache
Merge pull request #264 from aburgel/use_shared_cache

Change SDWebImageManager to use shared image cache
Do not mark URLs a fail when error is due to missing network connection
Don't dispatch cancelAll calls. 

- should fix pre-fetcher problems #247
- cancelAll should be always called using the main thread
Merge pull request #268 from matej/prefetcher-fix

Don't dispatch cancelAll calls.
Merge pull request #260 from kawanet/master

isRunning method added at SDWebImageManager
Add imageFromMemoryCacheForKey: method to synchronously query the memory cache (fix #263)
Fix podspec (fix #253)
Fixed bug where NSInvalidArgumentException was thrown if an image with a nil URL was downloaded.
Removed creation of NSError when a nil URL is downloaded.