manopapad/proper — pull request #79 by aerosol (2013-11-28 18:23:04+00:00)
Title: Fix checking for bitstring instance

For the following spec:

```
-spec foo() -> <<_:16>>.
foo() ->
<<"ab">>.
```

`check_typespecs` was failing, due to invalid assumption in `Unit` guards, with:

```
An exception was raised: error:badarith.
Stacktrace: [{proper_typeserver,is_instance,4,
[{file,"src/proper_typeserver.erl"},
{line,1318}]},
{proper_typeserver,'-apply_spec_test/5-fun-0-',6,
[{file,"src/proper_typeserver.erl"},
{line,509}]},
{proper,apply_args,3,[{file,"src/proper.erl"},{line,1359}]},
{proper,child,3,[{file,"src/proper.erl"},{line,1398}]},
{proper,'-spawn_link_migrate/1-fun-1-',2,
[{file,"src/proper.erl"},{line,675}]}].
```