syslog: split Unix domain support from network support.

This is to make it easier to support Solaris syslog.  On
Solaris syslog messages are sent via STREAMS using putmsg to
/dev/conslog.  The putmsg call uses a a control buffer of type
log_cdtl and a data buffer which is the message, and it is in
general a big mess.  This CL just splits out the Unix domain
support so that Solaris can use a different mechanism.  I do
not propose to implement the Solaris support today.  This
split will make it possible for gccgo to just call the libc
function for now.

R=r, rsc
CC=golang-dev
https://golang.org/cl/4261061

src/pkg/syslog/syslog_unix.go

@@ -0,0 +1,31 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package syslog
+
+import (
+	"net"
+	"os"
+)
+
+// unixSyslog opens a connection to the syslog daemon running on the
+// local machine using a Unix domain socket.
+
+func unixSyslog() (conn serverConn, err os.Error) {
+	logTypes := []string{"unixgram", "unix"}
+	logPaths := []string{"/dev/log", "/var/run/syslog"}
+	var raddr string
+	for _, network := range logTypes {
+		for _, path := range logPaths {
+			raddr = path
+			conn, err := net.Dial(network, "", raddr)
+			if err != nil {
+				continue
+			} else {
+				return netConn{conn}, nil
+			}
+		}
+	}
+	return nil, os.ErrorString("Unix syslog delivery error")
+}