Several bug fixes. Now that tokens have a mutable element, reference var sets, they...

Several bug fixes.  Now that tokens have a mutable element, reference var sets, they must be deep copied when merging table to avoid altering two tables with one operation.  A bug in removal by temp prevented sese-var mapping from being updated also.  A change in table implementation makes a difference between public and private ops like add and remove.  Any public op calls the private version and then asserts consistency.  Private versions can be called in more complex operatios and don't necessarily have to leave the table consistent until the bigger op is finished.  Much easier to find source of bugs this way.