(handle_key): For debugging, print information about

(handle_key): For debugging, print information about
alias key.
(filter): Add an alias for Meta and Alt modifiers.
(Mcond, Mplus, Mminus, Mstar, Mslush, Mand, Mor, Mnot): New
variables.
(minput__init): Initialize them.
(parse_expression): New function.
(resolve_expression): New function.
(parse_action_list): Handle expressions by parse_expression.
(take_action_list): Handle expressions by resolve_expression.