Mark bpchareq not hashjoinable, since it strips trailing blanks

before comparison; if fields being joined are different widths then hashing
will yield wrong answer.  Also, remove hashjoinable mark from all uses of
array_eq, because array structures may have padding bytes between elements
and the pad bytes are of uncertain content.  This could be revisited if
array code is cleaned up.
Modify opr_sanity regress test to complain if array_eq operator is marked
hashjoinable.