Gccgo was erroneously marking Call results as addressable, which led to
an obscure bug using text/template, as text/template calls CanAddr to
check whether to take the address of a value when looking up methods.
When a function returned a pointer, and CanAddr was true, the result was
a pointer to a pointer that had no methods.

Fixed in gccgo by https://golang.org/cl/21908.  Adding the test here so
that it doesn't regress.

Change-Id: I1d25b868e1b8e2348b21cbac6404a636376d1a4a
Reviewed-on: https://go-review.googlesource.com/21930
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>