-getSize now returns an `unsigned long long`.

This type now matches the type and width of the value returned by the
`fileSize` accessor of the `NSDictionary (NSFileAttributes)` category
(which is what is used when accumulating the total cache size).
Merge pull request #352 from jparise/getSize-return-type

-getSize now returns an `unsigned long long`.
Remove double import for SDWebImageDecoder.h
Merge pull request #355 from u16suzu/fix_double_import

Remove double import for SDWebImageDecoder.h
Added auto release pool to keep memory foot print down when retrieving image from disk in queryDiskCacheForKey