fix error and warning
convert to ARC
updated SDWebImage v3.4
Merge branch 'FixWarningAndConvertToARC' of github.com:hgia1234/MWPhotoBrowser

Conflicts:
	Demo/PhotoBrowserDemo.xcodeproj/project.pbxproj
	MWPhotoBrowser/Classes/MWPhoto.m
	MWPhotoBrowser/Libraries/SDWebImage/SDWebImageDownloader.m
convert demo to ARC
Merge remote-tracking branch 'i0xbean/master'

Conflicts:
	MWPhotoBrowser/Classes/MWPhoto.m
	MWPhotoBrowser/Classes/MWPhotoBrowser.m
	MWPhotoBrowser/Libraries/SDWebImage/SDWebImageDownloader.h
	MWPhotoBrowser/Libraries/SDWebImage/SDWebImageDownloader.m
	MWPhotoBrowser/Libraries/SDWebImage/SDWebImagePrefetcher.m