Change to command-line switches

Author: Arnd R. Strube

manual.markdown

@@ -251,7 +251,7 @@ Combining one -xg parameter with one -xn parameter will run only those tests tha
 
 Combining -s|sg with -xn, or -s|sn with -xg will run only those tests that satisfy both criteria.
 
-Specifying -xg or -xn in other combinations results in undefined behavior.
+Specifying several -xg or -xn with each other or in other combinations has no effect.
 
 *NOTE* Be careful with *-p*: