src/url.php: Avoid PHP warning in call to 'takeQuery' if URL has no query component; add function 'takePathAndQuery'.
test/url.php: Add some tests over 'takePath'.
src/test/: Add mock-sendmail.php, the beginnings of a helper-lib for "mocking out" email sending when running a test suite; not too much useful here so far, but should be more to come.
src/test/webapp.php: Add support to 'clickLink' for following a link containing a full URL, so long as that URL points to the domain under test (as specified by the 'domain' method of the test-harness).