The "${new=$old}" syntax only works for an undefined 'new', not for an empty one. I knew that. Really. I'm not stupid.
Now "git checkout xyzzy" will check out branch "xyzzy" and switch the HEAD to it.
And fix braino on testing "-f".
It is careful by default and refuses to overwrite old info, but if you want to force everything to be re-read, use the "-f" flag. Some day I'll make it take individual filenames too. Right now it's all-or-nothing.
