Setup : only scan necessary dirs for extensions

We were browsing the whole hierarchy but only the root module dir was needed
This could be slow (especially when developing with a .git dir)

setup/extensionsmap.class.inc.php

@@ -244,11 +244,13 @@ class iTopExtensionsMap
 	}
 	
 	/**
-	 * Read (recursively) a directory to find if it contains extensions (or modules) 
+	 * Read (recursively) a directory to find if it contains extensions (or modules)
+	 *
 	 * @param string $sSearchDir The directory to scan
 	 * @param string $sSource The 'source' value for the extensions found in this directory
 	 * @param string|null $sParentExtensionId Not null if the directory is under a declared extension
-	 * @return boolean
+	 *
+	 * @return boolean false if we cannot open dir
 	 */
 	protected function ReadDir($sSearchDir, $sSource, $sParentExtensionId = null)
 	{
@@ -260,6 +262,8 @@ class iTopExtensionsMap
 		    {
 		        // We're not recursing, let's add the directory to the list of scanned dirs 
 		        $this->aScannedDirs[] = $sSearchDir;
+
+			    return true;
 		    }
 			$sExtensionId = null;
 			$aSubDirectories = array();