Fix a few problems with the _Printer class and the license variable.

Fix a few problems with the _Printer class and the license variable.

1. repr(license) will no longer print to stdout and read from stdin;
you have to use license().  `license` is a short message explaining
this.

2. Use lazy initialization so that startup isn't slowed down by the
search for the LICENSE file.

3. repr(license) actually returns the desired string, rather than
printing to stdout and returning ''.  (Why didn't we think of this
before?)

4. Use the pythonlabs license URL as the license fallback instead of
the CNRI license handle.