The issue and fix are described in https://github.com/tmux-plugins/tmux-continuum/issues/16 .
Without this change, tmux-continuum works only for one tmux server on the machine. In a multi-user environment (e.g. a shared server), when multiple users are running their own tmux servers, this means that tmux-continuum works only for one of the users.
This change enables tmux-continuum for one tmux server per user instead of one tmux server per machine.
Do not count `tmux source-file .tmux.conf` as a tmux process when checking if
other tmux server is running.
Previously, this caused interpolation command not to be inserted into
`status-right` because `tmux source-file` was falsely detected as another tmux
server.