* Attribute infrastructure -- static design. Documentation is coming.

* Attribute infrastructure -- static design.  Documentation is coming.
  See test/unit/expr/node_white.h for use examples, including how to
  define new attribute kinds.

Also:

* fixes to test infrastructure
* minor changes to code formatting throughout
* attribute tests in test/unit/expr/node_white.h
* fixes to NodeManagerScope ordering
* use NodeValue::getKind() to properly deal with UNDEFINED_KIND
  (removing compiler warning)
* ExprManager: add proper NodeManagerScope to public-facing member
  functions
* store variable names and types in attributes
* SoftNode is a placeholder, not a real implementation