lockmode_t: Contention time may be equal

For some reason this was only a problem on Windows

Change-Id: I8699d51dfb827cd8b54735b78bba631c1e222203
Reviewed-on: http://review.couchbase.org/35168
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Volker Mische <volker.mische@gmail.com>