Support GE non-HFS DTI bvec

[mr-jaemin]

While current dcm2niix generates the following message for GE non-HFS (i.e. feet-first) DTI,
"GE DTI directions require head first supine acquisition"
Diffusion gradient vector (*.bvec) will be generated without any required conversion. So, bvec will be inaccurate as shown below

This pull request enables the geCorrectBvecs() routine for GE non-HFS DTI with the following warning message:
"Limited validation for non-HFS (Head first supine) GE DTI: confirm gradient vector transformation"

The bvec conversion for non-HFS would be same as HFS on GE based on this validation dataset:
Both Head-first and feet-first Knee DTI with both freq. encoding directions: RL and AP collected on the same volunteer within the same exam.

[neurolabusc]

@mr-jaemin thanks. I had submitted a much larger set of conflicting commits to the development branch. I have now applied your fix directly, so this PR has been effectively merged.