doc/go1.4.txt: unsafe is outside go1 compatibility guarantees

CC=golang-codereviews
https://golang.org/cl/164770043

doc/go1.4.txt

@@ -24,6 +24,7 @@ bufio: handling of empty tokens at EOF changed, may require scanner change (CL 1
 compress/flate, compress/gzip, compress/zlib: Reset support (https://codereview.appspot.com/97140043)
 crypto/tls: add support for ALPN (RFC 7301) (CL 108710046)
 crypto/tls: support programmatic selection of server certificates (CL 107400043)
+encoding/asn1: optional elements with a default value will now only be omitted if they have that value (CL 86960045)
 flag: it is now an error to set a flag multiple times (CL 156390043)
 fmt: print type *map[T]T as &map[k:v] (CL 154870043)
 encoding/csv: do not quote empty strings, quote \. (CL 164760043)
@@ -47,6 +48,6 @@ testing: add TestMain support (CL 148770043)
 text/scanner: add IsIdentRune field of Scanner. (CL 108030044)
 text/template: allow comparison of signed and unsigned integers (CL 149780043)
 time: use the micro symbol (µ (U+00B5)) to print microsecond duration (CL 105030046)
-encoding/asn1: optional elements with a default value will now only be omitted if they have that value (CL 86960045)
+unsafe: document the existing situation that unsafe programs are not go1-guaranteed (CL 162060043)
 
 go.sys subrepo created: http://golang.org/s/go1.4-syscall