fix min/mag filter etc.

* fixes a typo in the previous naming of GL_TEXTURE_MAG  "maxFilter" ->"magFilter"
* ofTexture::allocate() will allow NPOT textures if possible (also for iOS) - we check against the min/magFilters and the correct wrapping, falling back to nextPoT if necessary.

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>