hey @arturoc,

my thinking was that internally the ofFbo is created as before,
each texture is added in order using push_back().

the new method, `createAndAttachTexture(ofTexture & tex, GLenum internalFormat, GLenum attachmentPoint)`
can then be used after the ofFbo is allocated to swap out one of the ofTextures for an external ofTexture.

think that is the least intrusive way of doing it without changing the way ofFbo currently works.
let me know if you have any other ideas on how this should be done?