Add possibility to retrieve extension version
There's no way to determine the version of an installed extension though the API.
If an extension's behaviour relies on a specific version of another extension, it has to retrieve the version of the related extension manually ( e.g. https://svn.typo3.org/TYPO3v4/CoreProjects/feedit/trunk/feeditadvanced/ext_localconf.php checking for templavoila)...
Attached patch resolves that by adding the getExtVersion() to t3lib_extmgm...
(issue imported from #M13697)