[FSL] Updated BEDPOSTX and XFibres

Old interfaces are still available as OldBEDPOSTX and OldXFibres
fixed gradient nonlinearities implementation
fixed errors
fixed bug
fixed XFibres
fix doctest of BEDPOSTX
tested new XFibres. new parallel workflow
preparing new workflow for parallel processing
new split and merge interfaces
added test and some missing files in last commit
new parallel bedpostx finished :)
new naming conventions
Merge branch 'master' into enh/UpdateBEDPOSTX

Conflicts:
	CHANGES
	nipype/algorithms/misc.py
	nipype/interfaces/freesurfer/utils.py
bedpostx_parallel avoid computation of dyads uncertainty available
Interface Merge for large files
Merge branch 'enh/UpdateBEDPOSTX' of github.com:oesteban/nipype into enh/UpdateBEDPOSTX
fix missing comma
added computation of mean f samples in bedpostx
fix missing connections
fixed several bugs. tested in practice