doc/codewalk/functions.xml: Fix broken function examples

I removed the broken function comparison example and fixed a code highlighting regexp.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/5501078

doc/codewalk/functions.xml

@@ -45,7 +45,7 @@
   turn.
 </step>
 
-<step title="Multiple return values" src="doc/codewalk/pig.go:/\/\/ roll returns/,/stay.*true\n}/">
+<step title="Multiple return values" src="doc/codewalk/pig.go:/\/\/ roll returns/,/true\n}/">
 	Go functions can return multiple values.  
 	<br/><br/>
 
@@ -82,16 +82,6 @@
   associated with the current player.
 </step>
 
-<step title="Comparing functions" src="doc/codewalk/pig.go:/if action/,/currentPlayer\)\)\n\t\t}/">
-	Functions can be compared for equality in Go.  From the 
-	<a href="http://golang.org/doc/go_spec.html#Comparison_operators">language specification</a>:
-  Function values are equal if they refer to the same function or if both are <code>nil</code>.
-	<br/><br/>
-
-  We enforce that a <code>strategy</code> function can only return a legal
-  <code>action</code>: either <code>roll</code> or <code>stay</code>.
-</step>
-
 <step title="Simulating a tournament" src="doc/codewalk/pig.go:/\/\/ roundRobin/,/gamesPerStrategy\n}/">
 	The <code>roundRobin</code> function simulates a tournament and tallies wins.
 	Each strategy plays each other strategy <code>gamesPerSeries</code> times.

doc/codewalk/pig.go

@@ -61,9 +61,6 @@ func play(strategy0, strategy1 strategy) int {
 	currentPlayer := rand.Intn(2) // Randomly decide who plays first
 	for s.player+s.thisTurn < win {
 		action := strategies[currentPlayer](s)
-		if action != roll && action != stay {
-			panic(fmt.Sprintf("Player %d is cheating", currentPlayer))
-		}
 		s, turnIsOver = action(s)
 		if turnIsOver {
 			currentPlayer = (currentPlayer + 1) % 2