This (biggish) commit generalises the rotation modes functionality added for Bones, allowing Objects to use the various Euler Rotation orders, Axis-Angle, and Quaternion rotation representations.
I've also cleaned up the nomenclature of the rotation-related settings so that the naming styles are more consistent with each other. Unfortunately, this will break all files involving object or bone rotation animation made in 2.5 versions (2.4x will still get correctly converted).
General Notes:
* By default, Objects still default to using Eulers, while Bones will use Quaternions by default still.
* I've fixed all areas that I'm currently aware of to work with these changes. However, there are probably a few places where I've missed a few changes (i.e. auto-keyframing will need attention later).
* Removed the old "IPO-Keys" stuff from Transform code. I'm unlikely to restore this in the near future, and trying to fix that to include support for this commit would have been too much work.
