allow force activation of already active ports

[RJVB]

Allows to use port -f activate foo to activate (reactivate) ports that are already active. Useful as a shortcut to port deactivate foo && port activate foo when that operation is required, but also when activating multiple ports e.g. when one or more already turn out to have the desired variant/version activated.

[RJVB]

The selection list was shown twice if multiple versions/variants of a port are installed and the active one selected. Fixed.