single argument panic

note that sortmain.go has been run through hg gofmt;
only the formatting of the day initializers changed.
i'm happy to revert that formatting if you'd prefer.

stop on error in doc/progs/run

R=r
CC=golang-dev
https://golang.org/cl/850041
diff --git a/test/chan/doubleselect.go b/test/chan/doubleselect.go
index 53dafeb..592d2f5 100644
--- a/test/chan/doubleselect.go
+++ b/test/chan/doubleselect.go
@@ -56,7 +56,8 @@
 			break
 		}
 		if _, ok := seen[v]; ok {
-			panic("got duplicate value: ", v)
+			println("got duplicate value: ", v)
+			panic("fail")
 		}
 		seen[v] = true
 	}