updated TARGET_OF_IPHONE guard to TARGET_OF_IOS

ofOpenALSoundPlayer was still using TARGET_OF_IOS guard which is
deprecated,
have updated to TARGET_OF_IOS.
Merge pull request #3072 from julapy/ios_targets

updated TARGET_OF_IPHONE guard to TARGET_OF_IOS
remove glGetString that can return NULL

closes #2824
Merge branch 'master' of https://github.com/openframeworks/openFrameworks
removed unused clear()

closes #2600
Merge branch 'master' of https://github.com/openframeworks/openFrameworks