text/template: wrong name in error message

<pre><a href="http://play.golang.org/p/9nx1qVOyfT">http://play.golang.org/p/9nx1qVOyfT</a>

The error should say main:4, but it says foo:4.
The {{define &quot;foo&quot;}} has replaced the file name but
not reset the line number.  (Keeping the original file
name would be a more helpful error than resetting
the line number.)</pre>
