changed substr call, as it actually requires (initial position, length)

NOT (initial position, final position)

options.cc

@@ -23,9 +23,9 @@ bool BaseOption::matches(const string& arg)
 {
   string::size_type pos = 0, np;
   while((np = key_.find(",", pos)) != string::npos) {
-    if(arg == key_.substr(pos, np))
+    if(arg == key_.substr(pos, np - pos))
       return true;
-    pos = np+1;
+    pos = np + 1;
   }
   if(arg == key_.substr(pos, string::npos))
     return true;