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

Conflicts:
	Demo/PhotoBrowserDemo.xcodeproj/project.pbxproj
	MWPhotoBrowser/Classes/MWPhoto.m
	MWPhotoBrowser/Libraries/SDWebImage/SDWebImageDownloader.m