Support globs in run-tests.py#TESTS.

This means that there is no longer a need to add every individual test
to the list; only new *directories* have to be mentioned.  New tests
can be added just by dropping .js files into appropriate directories.

Tests which are not meant to be run by default now live in tests/manual/.
Currently there is one such test, tests/manual/standards/ecma-test262.js,
which downloads and runs the ECMAScript conformance suite.

Ongoing work on issue #12439.
Improvements to logic in FileHandler.translate_path.

We already have 'base_path' as a global variable, so use that (or rather,
a new derivative of that) instead of inspect.getfile(inspect.currentframe()).

Rather than splitting the path and then iterating over every component
trying to figure out if it's "special", take advantage of the fact that
posixpath.normpath() will reliably produce a path with all ../ and bare-/
components at the very beginning.  Preserve the distinction between paths
with and without a trailing /, as SimpleHTTPRequestHandler expects.

So that paths containing unusual (e.g. non-ASCII, non-UTF-8) segments can
safely be tested, unquote and then requote the entire path.  This means
that the *bytes* corresponding to the ASCII characters

  0123456789 ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz -_./

are guaranteed to be unquoted, and all other *bytes* are guaranteed to be
%-quoted.  (Note especially that *whether or not* the tests are being run
on Windows, \ in the original URL will be represented as %5C, and will
*not* be treated as a pathname separator.)

So that the tests behave consistently whether or not the OS has a case-
sensitive filesystem, after the above transformation, lowercase the entire
path.

Ongoing work on issue #12439.
Support Python scripts in test/www/.

Rather than add all the special URLs we'll ever want to run-tests.py,
the embedded HTTP server now supports scripts in test/www/.  If you
try to load http://localhost:9180/path and test/www/path doesn't exist
but test/www/path.py does, then test/www/path.py is loaded as a module.
That module must export one function, handle_request(), which is called
to produce the response.

handle_request() has the same semantics as
SimpleHTTPRequestHandler.send_head().  That is, it takes one argument,
the SimpleHTTPRequestHandler object, conventionally named 'req'.
It should call the send_response(), send_header(), and end_headers()
methods of that object as appropriate.  And it should return a readable
filelike whose contents are taken as the body of the response.

If either module import or handle_request() throws any exception, the
HTTP response will be a 500 Internal Server Error with body provided
by cgitb.

Ongoing work on issue #12439.
Add support for selective test execution.

If there are any positional arguments to test/run-tests.py, they are matched
(verbatim, not as regular expressions) against each test's name.  Only those
tests whose names contain at least one of the positional arguments will be
run.  Thus, for instance, you can run just the webpage tests with

    ./test/run-tests.py module/webpage

or one specific test with

    ./test/run-tests.py exact/name/of/test.js

or the basics and standards tests with

    ./test/run-tests.py basics standards

If no tests at all match, run-tests.py will print "ALL TESTS SKIPPED" and
exit unsuccessfully.

Ongoing work on issue #12439.