Shuffle http related test code. Hopefully it ends up at the right place :)
* bzrlib/tests/HttpServer.py: New file. bzrlib.tests.ChrootedTestCase use HttpServer. So the class can't be defined in bzrlib.tests.HTTPUtils because it creates a circular dependency (bzrlib.tests.HTTPUtils needs to import bzrlib.tests).
* bzrlib/transport/http/_urllib.py: Transfer test server definition to bzrlib.tests.HttpServer. Clean up imports.
* bzrlib/transport/http/_pycurl.py: Transfer test server definition to bzrlib.tests.HttpServer. Clean up imports.
* bzrlib/transport/http/__init__.py: Transfer all test related code to either bzrlib.tests.HttpServer and bzrlib.tests.HTTPUtils. Fix all use of TransportNotPossible and InvalidURL by prefixing it by 'errors.' (this seems to be the preferred way in the rest of bzr). Get rid of unused imports.
* bzrlib/tests/test_transport.py: (ReadonlyDecoratorTransportTest.test_local_parameters, FakeNFSDecoratorTests.test_http_parameters): Use HttpServer from bzrlib.tests.HttpServer instead of bzrlib.transport.http.
* bzrlib/tests/test_sftp_transport.py: (set_test_transport_to_sftp): Use HttpServer from bzrlib.tests.HttpServer instead of bzrlib.transport.http.
* bzrlib/tests/test_selftest.py: (TestTestCaseWithTransport.test_get_readonly_url_http): Use HttpServer from bzrlib.tests.HttpServer instead of bzrlib.transport.http.
* bzrlib/tests/test_repository.py: Does *not* use HttpServer.
* bzrlib/tests/test_http.py: Build on top of bzrlib.tests.HttpServer and bzrlib.tests.HTTPUtils instead of bzrlib.transport.http.
* bzrlib/tests/test_bzrdir.py: (ChrootedTests.setUp): Use HttpServer from bzrlib.tests.HttpServer instead of bzrlib.transport.http.
* bzrlib/tests/branch_implementations/test_http.py: (HTTPBranchTests.setUp): Use HttpServer from bzrlib.tests.HttpServer instead of bzrlib.transport.http.
* bzrlib/tests/branch_implementations/test_branch.py: (ChrootedTests.setUp): Use HttpServer from bzrlib.tests.HttpServer instead of bzrlib.transport.http.
* bzrlib/tests/__init__.py: (ChrootedTestCase.setUp): Use HttpServer from bzrlib.tests.HttpServer instead of bzrlib.transport.http.