Installation procedures:

Either build an egg:

    python setup.py bdist_egg

or use development environment:

    python setup.py develop -mxd $TRAC_ENV/plugins

Add to trac.ini configuration for plugin (use any valid states as needed):

    [changeset-validator]
    valid_ticket_states = accepted, assigned

Enable plugin in trac.ini

    [components]
    ...
    changesetvalidator.* = enabled

pre-receive and post-receive files use env variables TRAC_ENV and REPO_NAME
by default TRAC_ENV='../trac_env', REPO_NAME='(default)'
Copy (or link) them to the git repository "hooks" directory to use default values
Else (for example, when you have multiple repositories or different env location) create your own hooks
Those hooks should export TRAC_ENV and REPO_NAME and call post-receive.py or pre-receive.py