Plan: do away with shell scripts, and un-hard-wire the path /usr/local/lib/mercurial-server.

Done:

- move all modules into mercurial_server directory
- make mercurial_server.paths module; a function sets a global based on sys.argv[0]
- reduce hg-ssh-wrapper to nothing by moving all functionality into hg-ssh
- same for refresh-auth
- move most of do-refresh-auth into a module
- give that module a hook, and call the hook instead of the exe
- abolish refresh-auth shell script and rename do-refresh-auth to refresh-auth
- replace env vars with Python globals

Todo:

- change refresh-auth to refer to hg-ssh directly, abolish hg-ssh-wrapper
- add comment check and -f flag to refresh-auth
- change install script to a Python script, abolishing hginit