Raise an exception when reconfiguring objects that already exist.

Instead of silently discarding the reconfiugration method call, an
exception should be raised so the developer knows that they have
probably made a mistake somewhere.

This behavior is applied to helpers/components/behaviors but not other
registry types as those are less frequently reconfigured.

Refs #4693
Implemented the __xn() function
Implemented __dx() function
Implemented the __dxn() translation function
Removing unneded matches in ExtractTask
Consolidate duplicated code and fix a few issues.

* Fixup the message to be more generic.
* Exclude 'enabled' from config comparison. Components are often loaded
  by other components with enabled=false which should not cause errors.
* Fix loggers being rebuilt each time a config is defined and used.
Fix risky tests.

Failing to close output buffers makes PHPUnit unhappy. Switch to test
styles that allow all created buffers to be closed.
Fix more risky tests.

These buffer starts offset the buffer closes that are in the test that
is being invoked with run() in the test method.
Fixed CS error
Merge pull request #4751 from cakephp/fix-risky-tests

Fix risky tests
Merge pull request #4749 from cakephp/3.0-translation-context

3.0 translation context
Merge pull request #4750 from cakephp/issue-4693-duplicate-load

Fix duplicate load in registrys
Update version number to 3.0.0-beta2
Don't underscore plugin and controller names when generating form url.
Merge pull request #4754 from cakephp/3.0-formhelper

Don't underscore plugin and controller names when generating form url.
Fixed composer.json for the Datasource namespace
Add DashedRoute class.
Fix docblocks.
Remove unused constant.
Remove unused LOG_ERROR constant.

This constant has no other uses in cakephp/cakephp or in cakephp/app.
I'm pretty sure it is entirely unused at this point.
Remove unused TESTS constant