Use ScopedColor in gl::drawCoordinateFrame().
migrate to Autorelease Pool Blocks

Requires Xcode 4.2 and will deploy to any OS X and iOS release as we are using manual retain and release.
Merge pull request #564 from pizthewiz/autorelease-pool-block

migrate to Autorelease Pool Blocks
Merge pull request #563 from paulhoux/drawCoordinateFrame-scoped-color

Use ScopedColor in gl::drawCoordinateFrame().
Orphaning existing element VBO to fix #561