Hello

The following patch adds a new functionality to vc-rcs-checkin:
The login user can be added optionally.

Rationale: suppose your files are under RCS version control and you
collaborate with somebody who does not use RCS. So when you check in his
changes, it comes in handy to add the user login. This way vc-annotate
distinguish between his and yours changes.

Of course you don't want this behavior always since the majority of a
typical RCS user are single managed and don't require to change the
user in every checkin. That is why I introduced some new variables and a
«toggling» function which allows to switch this feature on or off.

I find my implementation quite a kludge, so if somebody finds this
useful and wants to modify the code, please do.

Uwe Brauer