Fix two problems reported by "Denis S. Otkidach" <ods@fep.ru>:

1. Some browsers don't understand attribute values in single quotes,
   so always use double quotes.

2. An undefined variable was referenced in the error reporting code in
   parseSubstitution().  (The error reporting cannot be reached unless
   _subst_re is changed -- but it is still a bug. :-)

lib/python/TAL/TALDefs.py

@@ -172,8 +172,7 @@ def parseAttributeReplacements(arg):
 def parseSubstitution(arg, position=(None, None)):
     m = _subst_re.match(arg)
     if not m:
-        raise TALError("Bad syntax in substitution text: " + `onError`,
-                       position)
+        raise TALError("Bad syntax in substitution text: " + `arg`, position)
     key, expr = m.group(1, 2)
     if not key:
         key = "text"
@@ -215,7 +214,4 @@ import cgi
 _cgi = cgi
 del cgi
 def quote(s):
-    if '"' in s and "'" not in s:
-        return "'%s'" % _cgi.escape(s)
-    else:
-        return '"%s"' % _cgi.escape(s, 1)
+    return '"%s"' % _cgi.escape(s, 1)