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.

Maybe we should rewrite `lookupRecursive` , and configM4Exists scope was private any only be called by `lookup` and `lookupRecursive`.

There codes were dirty patches and workaround.

I don't reviewed original phpbrew codes  deeply that why i can't just using 'lookupRecursive(extName);`
at 
https://github.com/phpbrew/phpbrew/blob/develop/src/PhpBrew/Command/ExtensionCommand.php#L94