os: rename SyscallError.Errno to SyscallError.Err

This lets us get rid of the OS-dependent implementations
of SyscallError.  The name "Err" was chosen to match the
PathError type.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5651084

src/pkg/os/error.go

@@ -12,3 +12,21 @@ type PathError struct {
 }
 
 func (e *PathError) Error() string { return e.Op + " " + e.Path + ": " + e.Err.Error() }
+
+// SyscallError records an error from a specific system call.
+type SyscallError struct {
+	Syscall string
+	Err     error
+}
+
+func (e *SyscallError) Error() string { return e.Syscall + ": " + e.Err.Error() }
+
+// NewSyscallError returns, as an error, a new SyscallError
+// with the given system call name and error details.
+// As a convenience, if err is nil, NewSyscallError returns nil.
+func NewSyscallError(syscall string, err error) error {
+	if err == nil {
+		return nil
+	}
+	return &SyscallError{syscall, err}
+}

src/pkg/os/error_plan9.go

@@ -9,24 +9,6 @@ import (
 	"syscall"
 )
 
-// SyscallError records an error from a specific system call.
-type SyscallError struct {
-	Syscall string
-	Err     string
-}
-
-func (e *SyscallError) Error() string { return e.Syscall + ": " + e.Err }
-
-// NewSyscallError returns, as an error, a new SyscallError
-// with the given system call name and error details.
-// As a convenience, if err is nil, NewSyscallError returns nil.
-func NewSyscallError(syscall string, err error) error {
-	if err == nil {
-		return nil
-	}
-	return &SyscallError{syscall, err.Error()}
-}
-
 var (
 	Eshortstat = errors.New("stat buffer too small")
 	Ebadstat   = errors.New("malformed stat buffer")

src/pkg/os/error_posix.go

@@ -6,7 +6,7 @@
 
 package os
 
-import syscall "syscall"
+import "syscall"
 
 // Commonly known Unix errors.
 var (
@@ -49,21 +49,3 @@ var (
 	ETIMEDOUT    error = syscall.ETIMEDOUT
 	ENOTCONN     error = syscall.ENOTCONN
 )
-
-// SyscallError records an error from a specific system call.
-type SyscallError struct {
-	Syscall string
-	Errno   error
-}
-
-func (e *SyscallError) Error() string { return e.Syscall + ": " + e.Errno.Error() }
-
-// NewSyscallError returns, as an error, a new SyscallError
-// with the given system call name and error details.
-// As a convenience, if err is nil, NewSyscallError returns nil.
-func NewSyscallError(syscall string, err error) error {
-	if err == nil {
-		return nil
-	}
-	return &SyscallError{syscall, err}
-}