dashboard-frontend.c needs tweaking for c++

[Julian Satchell <j satchell eris qinetiq com>]

I have just managed to get an AbiWord front-end sort of working. 

AbiWord is c++, and complained about dashboard-frontend.c, because of
the tighter cast rules. I fixed it for my hack with a sprinkle of casts,
but it would be much better if somebody who actually knows c++ properly
tidied it up.

If nobody gets round to fixing it first, I will post my changes when(if)
I get permission to publish my work on the Abiword frontend; this might
take a few weeks.

Julian