- The DOMVisitor class is simplified a bit; it doesn't visit
  attributes for you and it doesn't define endVisitElement().

- The CopyingDOMVisitor class is fixed to cope with this; instead of
  endVisitElement() it defines and uses backUp(), with the same
  purpose.  It defines and uses copyAllAttributes() and
  copyAttribute() to deal with attributes.

- The TALVisitor class is refactored so that the processing of METAL
  and TAL attributes is done more orderly (I discovered
  getAttributeNS() :-).

- Used a different way to split parts into semicolon-separated parts
  with doubling used to quote semicolons.

- Sped up the macro indexer by using a recursive function with an
  explicit argument rather than a visitor class.

- Added a slot indexer that works the same way.  (The macro and slot
  indexers have a lot in common, but they're still so small that I
  didn't bother factoring it out.  Later.)

- The runtest.sh script now takes optional command line arguments
  (full pathnames of testfiles) to specify a set of tests to run.

- The timer.py script was adapted to use the new macroIndexer().