[BUGFIX] Link to manual of sysext "form" is not displayed in EM

The system extension "form" comes with a manual in
typo3/sysext/form/Documentation/Manual/en/manual.sxw. As the corresponding
'docPath' key is not defined in ext_emconf.php, the link to open this
manual in not shown in the Extension Manager.

Change-Id: Ia644d3dcebdc8e8909a0a54a760825028e637104
Fixes: #30444
Releases: 4.6
Reviewed-on: http://review.typo3.org/5476
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert

typo3/sysext/form/ext_emconf.php

@@ -31,6 +31,7 @@ $EM_CONF[$_EXTKEY] = array(
 	'author_company' => '',
 	'CGLcompliance' => '',
 	'CGLcompliance_note' => '',
+	'docPath' => 'Documentation/Manual/en',
 	'version' => '0.9.0',
 	'constraints' => array(
 		'depends' => array(