[muc-channel] timestamp is a time_t not a gint64
[muc-channel] timestamp is a time_t not a gint64

Cast to the correct type so that Gabble compiles correctly on 32-bit.

I propose fixing this properly by using either gint64 or GDateTime in Wocky,
but not tonight.

mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble