Test suit for nginx.

Use prove to run tests as one usually do for perl tests.  Individual tests
may be run as well.

Note: some tests may fail since they are for bugs not fixed in public code.

Note: tests run nginx listening on localhost, and currently this includes
following ports: 8080, 10025.

Currently each test creates it's own temporary directory and uses it for
logs etc.  One may instruct tests not to remove the temp directory (e.g.
for analysis of failed test) by setting LEAVE environment variable.