[facets] add missing DATA_URL javascript variable definition (closes #3230380)

views/basetemplates.py

@@ -61,6 +61,7 @@
     self.write_doctype()
     # explictly close the <base> tag to avoid IE 6 bugs while browsing DOM
     self._cw.html_headers.define_var('BASE_URL', self._cw.base_url())
+    self._cw.html_headers.define_var('DATA_URL', self._cw.datadir_url)
     w(u'<meta http-equiv="content-type" content="%s; charset=%s"/>\n'
       % (content_type, self._cw.encoding))
     w(u'<meta name="viewport" content="initial-scale=1.0; '