implemented atomic expr alloc in prsim back-end
values seem to propagate atomically
specialize fanin-printing of atomic expressions to look like:
	z = x | y
added missing atomic negation expression
name some enums
prsim: refactor out post-event messages
prsim: perm'd USE_WATCHPOINT_FLAG
little more prsim command refactoring
Merge branch 'master' into run-time-expressions
working atomic node update printing, but may not be in causality ordering
fixed atomic bool connection_policy: forgot to inherit some implicit attributes from substruct
updated why-analysis for atomic-node queries