Issue #1033818 by catch, Rob Loach, amateescu, sun: Move xmlrpc includes into xmlrpc.module.

Conflicts:
	core/modules/simpletest/tests/xmlrpc.test
	core/modules/simpletest/tests/xmlrpc_test.info
	core/modules/simpletest/tests/xmlrpc_test.module
	core/modules/system/system.api.php
	core/modules/system/tests/modules/xmlrpc_test/xmlrpc_test.info
	core/modules/system/tests/modules/xmlrpc_test/xmlrpc_test.module
	core/modules/system/tests/xmlrpc.test
	core/modules/xmlrpc/lib/Drupal/xmlrpc/Tests/XmlRpcValidatorTest.php
	core/modules/xmlrpc/tests/modules/xmlrpc_test/xmlrpc_test.info
	core/modules/xmlrpc/tests/modules/xmlrpc_test/xmlrpc_test.module
let backdrop find the xmlrpc tests again
added endpoints that are compatible with Drupal 7 and 8
adjusted tests to use new endpoint
Merge remote-tracking branch 'remotes/xmlrpc/master' into Remove_XML-RPC_and_move_to_contrib_module