set_local_db, toggle_after_line and set_dot_env now return a
FileChange (path + before/after line pairs) instead of (), and main
prints it after each toggle so 'up'/'down' shows exactly what the
program rewrote in each env file.
connections.env and local .env are transitioning from dotted keys
(ci.db.master.ip, connection) to upper-cased RCC_-prefixed keys
(RCC_CI_DB_MASTER_IP, RCC_CONNECTION). Both forms are matched and
toggled during the migration, so old branches keep working while
new ones use the new format.
mathias