doc: add log.SetOutput to go1.5.txt

Change-Id: I257211f10b334eb4828be96cd434d588bfb1a378
Reviewed-on: https://go-review.googlesource.com/3605Reviewed-by: Rob Pike <r@golang.org>

doc/go1.5.txt

@@ -9,7 +9,7 @@ crypto/cipher: clarify what will happen if len(src) != len(dst) for the Stream i
 crypto/elliptic: add Name field to CurveParams struct (https://golang.org/cl/2133)
 crypto/tls: change default minimum version to TLS 1.0. (https://golang.org/cl/1791)
 encoding/base64: add unpadded encodings (https://golang.org/cl/1511)
-log: add global Output function (https://golang.org/cl/2686)
+log: add SetOutput functions (https://golang.org/cl/2686, https://golang.org/cl/3023)
 net/http: support for setting trailers from a server Handler (https://golang.org/cl/2157)
 net/smtp: add TLSConnectionState accessor (https://golang.org/cl/2151)
 runtime, syscall: use SYSCALL instruction on FreeBSD (Go 1.5 now requires FreeBSD 8-STABLE+) (https://golang.org/cl/3020)