New `vecreg` test for basic/normal usage

unit_tests/fdt/vecreg/feedsRun.normal

+#!/usr/bin/env fslpython
+
+import os
+import sys
+
+from pathlib import Path
+
+from fsl.wrappers import vecreg
+
+
+def main():
+    fsldir        = Path(os.environ['FSLDIR'])
+    outdir        = Path(sys.argv[1])
+    indir         = Path(sys.argv[2])/'fsl_course_data'/'fdt2'
+    dyads         = indir/'subj1.bedpostX'/'dyads1.nii.gz'
+    std           = fsldir/'data'/'standard'/'MNI152_T1_2mm.nii.gz'
+    diff2std_warp = indir/'subj1.bedpostX'/'xfms'/'diff2standard_warp.nii.gz'
+
+    dyads_std = outdir/'dyads1_std.nii.gz'
+    vecreg(dyads, dyads_std, std, warpfield=diff2std_warp)
+
+
+
+if __name__ == '__main__':
+    main()