Test suite for nginx.

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

Tests assume that nginx sources are in directory nginx at the same level
as directory with tests, and nginx was already configured and built (i.e.
nginx binary available as ../nginx/objs/nginx from test directory).

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

Note: tests run nginx (and backend daemons if needed) listening on localhost.
Currently this includes following ports: 8025, 8026, 8080, 8081, 8110, 8111,
8143, 8144.

Tests for memcached required memcached itself and Cache::Memcached to be
installed.

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 TEST_NGINX_LEAVE environment
variable.