add mri_surf2vol wrap
added identity input to Surface2VolTransform
Merge https://github.com/stymy/nipype

Conflicts:
	nipype/interfaces/afni/preprocess.py
fixed pull request issues:
wrapping Surface2VolTransform,
-moved from preprocess.py to utils.py
-improved input descriptions
-renamed output suffix
fixed errors from DOCTEST, now OK.
Reformated inputs and added tests
Merge branch 'enh/mri_surf2vol'