Fix unstable test in select_parallel.sql
One test case added in 22d946b0f verifies the plan of a non-parallel
nestloop join. The planner's choice of join order is arbitrary, and
slight variations in underlying statistics could result in a different
displayed plan. To stabilize the test result, h
Add new error code for "file name too long"
This new error code, named file_name_too_long, maps internally to the
errno ENAMETOOLONG to produce a proper error code rather than an
internal code under errcode_for_file_access(). This error code can be
reached with some SQL command patterns, like a s
