Fix some more hashjoin-related bugs in pg_operator. Fix

Fix some more hashjoin-related bugs in pg_operator.  Fix
hashjoin's hashFunc() so that it does the right thing with pass-by-value
data types (the old code would always return 0 for int2 or char values,
which would work but would slow things down a lot).  Extend opr_sanity
regress test to catch more kinds of errors.