fix #254: make failed rigid rules not block late rules from executing.
fix #246: only let one rigid body rule apply to a cell at a time.

Also updated with a more complete test. The old test relied on
broken behavior related to #254.
fix #244: ban objects named "message", it confuses the parser.
simplify CellPattern.replace rigid logic
Merge pull request #255 from rmmh/master

more bugs