BF: spm_vol_check removed from SPM8; copy, fix

Use our own copy of spm_vol_check for compatibility.
TST: add gui check for design fill

It generates an error for the vol_check problem reported on the list.
RF: use SPM8 version of spm_vol_check

Only formatting differences between old and new version.
RF: remove executable bit on add_contrasts

Thanks to Dimitri Papadopoulos Orfanos for pointing that out.
Merge pull request #5 from matthew-brett/vol-check-fix

BF: spm_vol_check removed from SPM8; copy, fix

Use our own copy of spm_vol_check for compatibility.

Thanks to Dimitri Papadopoulos for pointing out the problem.