[Devel] need a way to check if transaction has been cancelled

[Juha Heinanen]

i have come to the conclusion that the easiest way to solve the
canceling problem that klaus reported is to have a function,
e.g. t_check_cancel(), that can be called in failure route and tells if
the transaction in question has been canceled by the uac. 

this way failure route would know to do nothing even if min reply code
from the branches would be something else than 487.

bogdan, is this function hard to implement?

-- juha