Oops!  databraid.eq was totally wrong.  Writing unit tests is good...
Oops 2!  databraid.eq was still not right.
Copy braid word first to avoid tcross errors in databraid.tensor.
Check for commuting blocks of generators in check_tcross.  Resolves issue #94 (again).
Added lots of unit tests for databraid, which uncovered several bugs (issues #93,#94,#95,#97,#98)!