document state variables, naming clean up, add dictionary for commit messages
only accept messages between low water mark, high water mark (see BFT p4-5)
seqno_in_bounds wrapper function
scaffolding for making checkpoints
cleanup, docs
implement make_checkpoint
view change progress
begin implementation of handle_checkpoint
merge checkpoint branch
Merge branch 'checkpoint' into view_change
small bugs
sig --> optional
fix bugs
everyone should handle pre_prepares!
view change timeout --> 2 secs
fix bug where primary ignored messages
if x is not None is not the same as if x
user and  application
user and  application
timer wrappers