Backs up the project database.

def backup(filename):
    """
    Backs up the project database.
    """
    tmp_file = "/tmp/%s" % filename
    # We dump to /tmp because user "postgres" can't write to other user folders
    # We cd to / because user "postgres" might not have read permissions
    # elsewhere.
    with cd("/"):
        postgres("pg_dump -Fc %s > %s" % (env.proj_name, tmp_file))
    run("cp %s ." % tmp_file)
    sudo("rm -f %s" % tmp_file)