doc: mention os/exec StdinPipe change in Go 1.2 doc
Fixes #6439.
R=r, minux.ma
CC=golang-dev
https://golang.org/cl/13478045
diff --git a/doc/go1.2.html b/doc/go1.2.html
index fcbf5e2..2dc90f8 100644
--- a/doc/go1.2.html
+++ b/doc/go1.2.html
@@ -824,6 +824,17 @@
</li>
<li>
+The <a href="/pkg/os/exec/"><code>os/exec</code></a> package's
+<a href="/pkg/os/exec/#Cmd.StdinPipe"><code>Cmd.StdinPipe</code></a> method
+returns an <code>io.WriteCloser</code>, but has changed its concrete
+implementation from <code>*os.File</code> to an unexported type that embeds
+<code>*os.File</code>, and it is now safe to close the returned value.
+Before Go 1.2, there was an unavoidable race that this change fixes.
+Code that needs access to the methods of <code>*os.File</code> can use an
+interface type assertion, such as <code>wc.(interface{ Sync() error })</code>.
+</li>
+
+<li>
The <a href="/pkg/runtime/"><code>runtime</code></a> package relaxes
the constraints on finalizer functions in
<a href="/pkg/runtime/#SetFinalizer"><code>SetFinalizer</code></a>: the
