Improve some Jingle error messages
Improve some Jingle error messages

It's silly to have more accurate information in a DEBUG message than you
send to the peer, for example. Also, kill off the (now-unused) SET_FOO()
error-setting macros --- they don't buy anything.

community-ssu/telepathy-gabble,jku/telepathy-gabble,mlundblad/telepathy-gabble,jku/telepathy-gabble,mlundblad/telepathy-gabble,community-ssu/telepathy-gabble,jku/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,community-ssu/telepathy-gabble,community-ssu/telepathy-gabble