Improve performance of rules templates by not calling the "and" function if there is only one condition.

src/calibre/library/coloring.py

@@ -62,14 +62,22 @@ class Rule(object):  # {{{
             return None
         conditions = [x for x in map(self.apply_condition, self.conditions) if x is not None]
         conditions = (',\n' + ' '*9).join(conditions)
-        return dedent('''\
-                program:
-                {sig}
-                test(and(
-                         {conditions}
-                    ), '{color}', '');
-                ''').format(sig=self.signature, conditions=conditions,
-                        color=self.color)
+        if len(self.conditions) > 1:
+            return dedent('''\
+                    program:
+                    {sig}
+                    test(and(
+                             {conditions}
+                        ), '{color}', '');
+                    ''').format(sig=self.signature, conditions=conditions,
+                            color=self.color)
+        else:
+            return dedent('''\
+                    program:
+                    {sig}
+                    test({conditions}, '{color}', '');
+                    ''').format(sig=self.signature, conditions=conditions,
+                            color=self.color)
 
     def apply_condition(self, condition):
         col, action, val = condition