A fix and an improvement to contrib/reindent.pl

I found myself adding tabs as indentation, which wasn't what I wanted; so fixed the script to disable indent-tabs-mode.  I was tempted to also untabify everywhere, but decided to leave that as a comment.
Purging dangling hspace at the same time seems a sensible bonus feature for this script, so I added it.
Hoping @tzz can still review this ...