It's not a group: must handle the inside as a sequence of literal chars,
not a single literal string.

That is, \Qab\E+ is the same as ab+, not (ab)+.

Fixes #11187.

Change-Id: I5406d05ccf7efff3a7f15395bdb0cfb2bd23a8ed
Reviewed-on: https://go-review.googlesource.com/17233Reviewed-by: David Crawshaw <crawshaw@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>