Cleaning up the loose ends

Many loose-end projects are marked by comments containing "XXX". Any of those you'd like to tackle are fair game.

Some other things that would be nice:

• Use const more consistently throughout the code.
• Use string in preference to char* where possible.
• Add the concept of test categories, assign each test to one or more of them, and add a way to run all the tests in a given category.
• Push the Test class hierarchy down one more level of detail. (I actually did this, factoring out everything that's common to classes like BasicTest, but it turned out to be more awkward to use than just cutting and pasting code, so I backed out the changes. After a few more tests are written, it should be more clear how to do this correctly.)
• Automated checks for memory leaks.
• GLX 1.3 support.