suggesting changes to `interfaces.base`

[djarecka]

Summary

I copy/paste my comments and questions from #2303, so might be included in a separate pr. Comments are welcome:

• is anyone using MpiCommandLine? couldn't find any examples in nipypehttps://github.com/oesteban/nipype/blob/ref/interface-base/nipype/interfaces/base/core.py#L1145

• _check_version_requirements does not check the max_version, this block has wrong indentation: https://github.com/oesteban/nipype/blob/ref/interface-base/nipype/interfaces/base/core.py#L403

• I was a bit confused about BaseFile and File, etc., do we really need both? Also I believe that we're assuming that BaseUnicode uses the fast validator (https://github.com/oesteban/nipype/blob/ref/interface-base/nipype/interfaces/base/traits_extension.py#L98), but from traits documentation I understood that Unicode (not BaseUnicode) uses the C-level fast validator (http://docs.enthought.com/traits/traits_api_reference/trait_types.html?highlight=baseunicode#traits.trait_types.BaseUnicode. Am I missing something?

• couldn't find a place where we're using _requires_warn (https://github.com/oesteban/nipype/blob/ref/interface-base/nipype/interfaces/base/specs.py#L114)

• the same about _hash_infile (https://github.com/oesteban/nipype/blob/ref/interface-base/nipype/interfaces/base/specs.py#L158)

• changing names to "list" https://github.com/oesteban/nipype/blob/ref/interface-base/nipype/interfaces/base/specs.py#L263

• is this method (https://github.com/oesteban/nipype/blob/ref/interface-base/nipype/interfaces/base/support.py#L171) still working?
  is it for this package: http://ipython.readthedocs.io/en/stable/api/generated/IPython.lib.pretty.html#extending ?
  they suggest _repr_pretty_

• should be called MultiObject instead of MultiPath? https://github.com/oesteban/nipype/blob/ref/interface-base/nipype/interfaces/base/traits_extension.py#L357

• should we keep only 2 classes InputMultiPath and OutputMultiPath (the first one doesn't have any new methods)?

updates

• refining and simplifying Bunch class (using hastraits)
• Check on this synchronize
• Check the logic of this