Unify error codes

Change-Id: I26c145ab66372120597db4c8c389ca7fcee86614
Scream on uncaughtException

Change-Id: Id7855ec03dacf22a3afefd728a90bc13f6abc930
oops: set CBExc.set_ when assigning

Change-Id: I3abad1bfb59c97da2db3f9b8c7aeb6d0b1e2d2b5
Make new 'Connection' class

Change-Id: Id79120eaa4bc179f5b9d4353bf3cb1461841f22e