DOC: added title parameter
NF: scatter plot between underlay and overlay intensity
BF: make sure that identity transformation works (to show examples of poor alignment)
RF+BK: chance "-o" parameter from overwrite to output directory, to conform to other command line functionality
ENH: raise an error if any command line commands fail. Addresses https://github.com/PyMVPA/PyMVPA/issues/139
Merge pull request #145 from nno/_tent/afni

minor improvements in prep-afni-surf while the whole destiny/future of this submodule is still unclear