Fixes extension list / enable /disable issues.

Fixes `phpbrew ext` `phpbrew ext [enable|disable]` not working correctly when extension source codes and config.m4 not in it's root directory.

haha.. i am in conference meeting.and these message was wrote by cellphone ... too much typo , sorry!

I mean , we should refactoring `look` and `lookRecursive` methods.
And `configM4Exists` 's accessibility should be `private` and only been called by `look` or `lookRecursive` .

`ExtensionCommand` calls `configM4Exists` and `createM4Extension` 
```
$dir = $extDir . DIRECTORY_SEPARATOR . $extName;
                if ($m4files = ExtensionFactory::configM4Exists($dir)) {
                    $this->logger->debug("Loading extension information $extName from $dir");

                    foreach ($m4files as $m4file) {
                        try {
                            $ext = ExtensionFactory::createM4Extension($extName, $m4file);
                            // $ext = ExtensionFactory::createFromDirectory($extName, $dir);
                            $extensions[$ext->getExtensionName()] = $ext;
                            $extensionNames[] = $extName;
                            break;
                        } catch(Exception $e) {

                        }
                    }
                }
```
should be rewrite to using `lookup` or `lookupRecursive` .

But, when i replaced above codes to `lookupRecursive($extName)`, it failed .