Accept only takes one argument, needs to detect error

[petersilva]

Lucie got bit by a copy/paste error where an accept clause in a sender had a space in it. It caused warnings not to get translated until we caught it.

accept clauses only take one argument. It would be good if sundew indicated (error message? fail to start up) when there is a clear syntax error in an accept, or a reject.

was: https://sourceforge.net/p/metpx/bugs/29/