checking OpenGL error flag before loading any texture

GLKTextureLoader always fails if 'glGetError()' is not clean -- even though the error actually happened somewhere else. So we better remove any pending error before initiating the loading process.
moved 'setCurrentController' from internal to public 'Sparrow' class interface
Merge branch 'master' into stable
raised version to 2.0.1
updated change log for v2.0.1
Merge branch 'master' into stable (forgot ChangeLog and version Macro in previous merge)
Added podspec and forwarding all view touches to sparrow handler
Merge remote-tracking branch 'upstream/stable' into stable
Merge branch 'master' of github.com:timrossinfo/Sparrow-Framework into stable
Updated podspec to 2.0.1