MAINT: 4DD extra prep does not require copy of radar
All is good!

I tested @jjhelmus' pr_175 branch, which sought to remove the
unecessary copying of all radar fields from my original PR to improve
velocity correction using the 4DD algorithm. After testing and
correcting some minor bugs (just typos), it looks like this PR is ready
to merge into Py-ART's master!
Merge branch 'jjhelmus-pr_175' into fourdd-prep