gob: split uses of gobError, remove unnecessary embedding

Will make gofix for error run more smoothly.
The overloading of gobError appears to be unintentional.

R=r
CC=golang-dev
https://golang.org/cl/5308060

src/pkg/gob/codec_test.go

@@ -41,7 +41,7 @@ var encodeT = []EncodeT{
 // plain test.Error call.
 func testError(t *testing.T) {
 	if e := recover(); e != nil {
-		t.Error(e.(gobError).Error) // Will re-panic if not one of our errors, such as a runtime error.
+		t.Error(e.(gobError).err) // Will re-panic if not one of our errors, such as a runtime error.
 	}
 	return
 }

src/pkg/gob/decoder.go

@@ -64,7 +64,7 @@ func (dec *Decoder) recvType(id typeId) {
 	dec.wireType[id] = wire
 }
 
-var errBadCount = gobError{os.NewError("invalid message length")}
+var errBadCount = os.NewError("invalid message length")
 
 // recvMessage reads the next count-delimited item from the input. It is the converse
 // of Encoder.writeMessage. It returns false on EOF or other error reading the message.

src/pkg/gob/error.go

@@ -18,7 +18,7 @@ import (
 
 // A gobError wraps an os.Error and is used to distinguish errors (panics) generated in this package.
 type gobError struct {
-	os.Error
+	err os.Error
 }
 
 // errorf is like error but takes Printf-style arguments to construct an os.Error.
@@ -29,14 +29,14 @@ func errorf(format string, args ...interface{}) {
 
 // error wraps the argument error and uses it as the argument to panic.
 func error(err os.Error) {
-	panic(gobError{Error: err})
+	panic(gobError{err})
 }
 
 // catchError is meant to be used as a deferred function to turn a panic(gobError) into a
 // plain os.Error.  It overwrites the error return of the function that deferred its call.
 func catchError(err *os.Error) {
 	if e := recover(); e != nil {
-		*err = e.(gobError).Error // Will re-panic if not one of our errors, such as a runtime error.
+		*err = e.(gobError).err // Will re-panic if not one of our errors, such as a runtime error.
 	}
 	return
 }