texture cache fix for ofxiOSVideoPlayer

ofTexture now supports using external texture IDs with this method,
setUseExternalTextureID
this PR updates ofxiOSVideoPlayer to work with this new method.
Merge pull request #2558 from julapy/ios-video-texture-cache-fix

texture cache fix for ofxiOSVideoPlayer
Merge branch 'master' of github.com:openframeworks/openFrameworks into Feature-VS2013