Store SMPP sequence number mapping before sending submit_sm PDU.
Merge branch 'develop' into feature/issue-780-better-SMPP-seq-num-handling
make DummySmppTransport less of a Dummy
Merge branch 'feature/issue-780-better-SMPP-seq-num-handling' into develop
Merge branch 'develop' of github.com:praekelt/vumi into develop