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/src/pkg/bufio/bufio.go b/src/pkg/bufio/bufio.go
index 9b52a36..1af9545 100644
--- a/src/pkg/bufio/bufio.go
+++ b/src/pkg/bufio/bufio.go
@@ -75,7 +75,7 @@
 	b, err := NewReaderSize(rd, defaultBufSize)
 	if err != nil {
 		// cannot happen - defaultBufSize is a valid size
-		panic("bufio: NewReader: ", err.String())
+		panic(err)
 	}
 	return b
 }
@@ -353,7 +353,7 @@
 	b, err := NewWriterSize(wr, defaultBufSize)
 	if err != nil {
 		// cannot happen - defaultBufSize is valid size
-		panic("bufio: NewWriter: ", err.String())
+		panic(err)
 	}
 	return b
 }