Pretty print debug messages
Fix bug in inner representation of receive
Minor refactoring
Revise sleep set blocking detection algorithm

Major changes:

* Always execute sleeping processes immediately after they are awakened
  (priorities.erl exposes a bug there).
* Initials are now working correctly on the 'speculative' test
  (etsi_2.erl)
* Do not reorder instructions that woke up others in the current trace
* Do not reorder anything until everything has woken up
Remove all sleep-set-blocking avoidance detection from algorithm

Some added tests showed that there were incorrect results (missed interleavings)
from the advanced features of the algorithm.

It's best to go back to correctess and think again about optimality.
Merge branch 'sa/correctness'