Generate package comment in alldocs.go using line comments rather than
general comments. This scales better, general comments cannot contain the
"*/" character sequence. Line comments do not have any restrictions on
the comment text that can be contained.

Remove the dependency on sed, which is not cross-platform, not go-gettable
external command.

Remove trailing whitespace from usage string in test.go. It's unnecessary.

Fixes #16030.

Change-Id: I3c0bc9955e7c7603c3d1fb4878218b0719d02e04
Reviewed-on: https://go-review.googlesource.com/23968Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>