ENH: Move ITKv4 towards 4.6.0rc20140719

ITKv4 was missing some shared library external declarations
as provided by Braley Lowekamp.  This patch includes those
externals so that the building of DWIConvert can again
succeed.
ENH: Update SimpleITK to be in sync with ITK

Recent additions for registration framework API changes
have been incorporated into recent versions of SimpleITK

Since ITK was updated, we should update SimpleITK to be
in sync with that version.
COMP: Provide Updates to BRAINSFit and DWIConvert

After the NAMIC meeting, several changes were made to address issues
with BRIANSFit and DWIConvert.