[ios] - support XCode 5.1.1 with iOS SDK 7.1

This makes XBMC compile on the current dev tools for iOS. (basically the updated clang 503.0.40 was the issue here).

@davilla for review ...

compile tested on jenkins (old xcode/sdk) and runtime tested on ios and atv2 (local compile with current xcode and sdk)...

thx @linusyang for the libmpeg2 patch