Dependencies from default productions aren't included in flow type inference

[krame505]

For example

inherited attribute inh::Integer occurs on Foo;
inherited attribute syn::Integer occurs on Foo;
aspect default production
top::Foo ::=
{ top.syn = top.inh; }

If there are no other equations for syn, this will flag the default equation as exceeding the flow type of syn. As a workaround, one can explicitly specify flowtype syn {inh} on Foo;.

[krame505]

Note that this isn't quite true - if there are non-forwarding productions that lack an equation for syn, then the dependencies of the default equation for syn will still have an effect. But if all non-forwarding productions have an equation, the flow type for syn will not be inferred to contain inh. This is an unusual situation with regular nonterminals (unless some non-forwarding prods still need to be written that will make use of the default equation), but for closed nonterminals this is a more egregious issue as one would frequently write new non-forwarding productions for the nonterminal in extensions, where the default would apply.

The fix here is to include default production flow graphs in the flow type inference process.