[PATCH] Change wait_time column of pg_stat_lock to double precision

Hi,

While looking at the lock-related code, I noticed that pg_stat_lock
is the only statistics view whose timing column (wait_time) uses
bigint.  Every other statistics view uses double precision for
measured-time columns.  I do not see a reason for pg_stat_lock to
differ.

The attached patch changes the column to double precision.

Regards,
Tatsuya Kawata