CCBC-244: [bconf_io] Don't be so liberal with maybe_breakout

Change-Id: I00d8ab6aa9d435aebcb9234665f70f2d16a2b8ab
Reviewed-on: http://review.couchbase.org/28341
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>