A smallish selection of already existing tests, run with
the indentation option.

The Maps implementation handles ?unit in more cases.

Exactly when t_is_none_or_unit() is to be called is not clear to me.
The added cases are about a map type being ?unit, but the key or the
value of an association can also be ?unit, but that is not always
checked.

Huge maps are truncated differently by the pretty printer. The reason
is that erl_types:is_singleton_type/1 no longer recognizes complex
singleton types, which results in a less precise representation of map
types.

The test case loop.erl shows that there is a problem with certain
singleton key types. Here the internal representation toggles between
 #{a | b => ...} and #{a => ..., b => ...}

The choice is to turn #{a | b => ...} into #{a => ..., b => ...} early
(t_from_form()). The aim is to keep as much info as possible (in
pairs). However, including complex singleton keys (tuples, maps) in
this scheme is potentially too costly, and a bit complicated. So one
more choice is made: let atoms and number (and nothing else) be
singleton types, and let complex keys go into the default key.

* maint:
  dialyzer: Increase time limit for tests
  dialyzer: Optimize typesig
  dialyzer: Optimize evaluation of complex code
  dialyzer: Optimize collection of variables

Conflicts:
	lib/dialyzer/src/dialyzer_typesig.erl

Suggested by Kostis.

Messages regarding guards with orelse/andalso could look
like "Clause guard cannot succeed. The variable A was matched
against the type any()". Now they look like as if or/and is
used: "Guard test is_integer(A::atom()) can never succeed".