erp5_forge: avoid business template build for VCS tab

by aborting the transaction after sending the diff tree to the user.
The diffs are still applied to the working copy.

bt5/erp5_forge/SkinTemplateItem/portal_skins/erp5_vcs/tree.xml.xml

@@ -63,6 +63,10 @@ if not root:\n
   return \'\'\'<?xml version=\'1.0\' encoding=\'UTF-8\'?>\n
 <tree id=\'0\'></tree>\'\'\'\n
 \n
+if REQUEST is not None: # XXX workaround to prevent zodb bloat (bt build)\n
+  # This script is mostly used by javascript, we can abort the transaction\n
+  REQUEST.RESPONSE.write(vcs_tool.treeToXML(root))\n
+  raise ValueError("Abort transaction")\n
 return vcs_tool.treeToXML(root)\n
 
 
@@ -70,7 +74,7 @@ return vcs_tool.treeToXML(root)\n
         </item>
         <item>
             <key> <string>_params</string> </key>
-            <value> <string>show_unmodified=False, do_extract=True</string> </value>
+            <value> <string>show_unmodified=False, do_extract=True, REQUEST=None</string> </value>
         </item>
         <item>
             <key> <string>id</string> </key>