script/*: fold $usage into $help, support `-h' instead of -?

script/*: fold $usage into $help, support `-h' instead of -?

`-h' doesn't conflict with anything, and some users (including
git users) may be more accustomed to using it rather than the
rarely-seen-outside-of-Getopt::Long `-?' switch.

We can also rely on the GetOptions() function to emit a proper
error message instead of just "bad command-line args".