Fix owner: search operator substring regression In prior releases the owner: and reviewer: operators performed substring searching to locate user accounts that match the argument, and find all changes relevant to those accounts. Fix the operators to perform that multiple-account searching again. Bug: issue 646 Change-Id: Ie0d67ad15ddffa7d2d774466c42f84dc1a760f25 Signed-off-by: Shawn O. Pearce <sop@google.com>