Sections 3.5 and 4.1.2 state that in-order delivery is required for reliable
messages with the same SID. 

Section 4.4.3 already handles the case that GIST stops using one MA and starts
using another, but can be extended to include the possibility of flushing the MA
with a Hello as well as gracefully closing the MA.

Section 4.3.3 should be extended to note that messages should not be distributed
in parallel over multiple MAs.