src/pkg/[a-m]*: gofix -r error -force=error

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/5322051
diff --git a/src/pkg/big/nat.go b/src/pkg/big/nat.go
index fa0d7e7..a46f782 100644
--- a/src/pkg/big/nat.go
+++ b/src/pkg/big/nat.go
@@ -19,8 +19,8 @@
 // and rationals.
 
 import (
+	"errors"
 	"io"
-	"os"
 	"rand"
 )
 
@@ -613,10 +613,10 @@
 // ``0x'' or ``0X'' selects base 16; the ``0'' prefix selects base 8, and a
 // ``0b'' or ``0B'' prefix selects base 2. Otherwise the selected base is 10.
 //
-func (z nat) scan(r io.RuneScanner, base int) (nat, int, os.Error) {
+func (z nat) scan(r io.RuneScanner, base int) (nat, int, error) {
 	// reject illegal bases
 	if base < 0 || base == 1 || MaxBase < base {
-		return z, 0, os.NewError("illegal number base")
+		return z, 0, errors.New("illegal number base")
 	}
 
 	// one char look-ahead
@@ -644,7 +644,7 @@
 						return z, 0, err
 					}
 				}
-			case os.EOF:
+			case io.EOF:
 				return z.make(0), 10, nil
 			default:
 				return z, 10, err
@@ -676,7 +676,7 @@
 		}
 
 		if ch, _, err = r.ReadRune(); err != nil {
-			if err != os.EOF {
+			if err != io.EOF {
 				return z, int(b), err
 			}
 			break
@@ -693,7 +693,7 @@
 		return z, 10, nil
 	case base != 0 || b != 8:
 		// there was neither a mantissa digit nor the octal prefix 0
-		return z, int(b), os.NewError("syntax error scanning number")
+		return z, int(b), errors.New("syntax error scanning number")
 	}
 
 	return z.norm(), int(b), nil