setup.sh- fix installation bugs

I had been wondering for a while why it wasn't quite working, and now I
know. I had been doing a few really stupid, nonsensical things to
generate paths.

I also added code to go ahead and make the .vim_backups directory to
keep vim from complaining since it seems incapable of making such a
directory itself.
vim- Fix vim directory creation issue

And once again, almost the exact same issue can be found in the vimrc
file. No wonder it couldn't create the .vim_backup directory in the
right place.

Sidenote- apparently glob will expand ~ into $HOME, and regular vim
won't. glob must either a. be like glob in Perl, actually using the
shell's glob, or b. act like the shell for some reason. It doesn't look
like this is documented. I guess it's just expected?