TYPO3 Core

Problem: ========
I have messed around with Ext Direct and have experimented a lack of debug output when things go wrong.

Consider the URL bellow which is the API Generator and is called for configuring Ext Direct on the client side. When Ext Direct is missconfigured somewhere, the URL bellow returns nothing. This is not optimal as it is quite tough to spot the flaw in this condition.

http://domain.tld/typo3/ajax.php?ajaxID=ExtDirect::getAPI&namespace=TYPO3.MyExtension

More info: http://wiki.typo3.org/index.php/ExtDirect#The_API_Generator

Solution: =========

I suggest to add:
- some debug output to give the developer clues about what can be wrong. Message is displayed on the javascript console or in prompt message when console is disabled
- add a "clear_cache" parameter for development context. The result of typo3/ajax.php is put into cache_hash for performance. But while coding, it is a bit annoying to clear the cache manually each time something change in your router server side.

Steps to reproduce: ===================

- Install extension "extdirecttest" http://bugs.typo3.org/file_download.php?file_id=10024&type=bug
- Make sure the extension is working properly.
- In ext_localconf.php search and replace every occurrence "TYPO3.Demo" by "TYPO3.WRONG"
- Clear the cache
- Reload the FE.

You should see an error message displayed on the javascript console or as prompt message if console is disabled.
(issue imported from #M14618)