A bug is fixed, but there are more problems.

Modify erl_types.erl like this:

  -define(EXPAND_LIMIT, 500).

and bogus warnings are output (again).

Callbacks and specs are compared (subtype) in dialyzer_behaviour. If
they are expanded to different depths, then invalid warnings can be
generated.

After introducing maps for supervisor flags and child specs two tests
in behaviour_SUITE started failing:

behaviour_SUITE:custom_sup - failed because the type of the Period
(MaxT) property had been changed (corrected) from non_neg_integer() to
pos_integer() in the specification of the init callback in
supervisor.erl

behaviour_SUITE:supervisor_incorrect_return - same as above, plus the
introduction of #{} as possible value for the supervisor flags and
child_specs.

To ensure that 'master' compiles when we merge 'maint' to it,
regardless of which encoding is default in 'master', all source
files with non-ascii characters *must* have the encoding specified.