Teach minishogi to issue "setup" command on variant selection.

This make gnuminishogi automatically switch XBoard to mini-Shogi, so
that the config file 'mini' is no longer needed, but a simple "xboard
-fcp gnuminishogi" is sufficient. (OK, that is not shorter than
"xboard @mini", but it is more logical, and don't requires people know
that a config file 'mini' exists.)

To play with oriental theme "xboard @shogi -fcp gnuminishogi" should
suffice.

YD: use "minishogi" instead of just "mini".
XBoard: split printing of the features line for clarity.