Issue 7462 - Error message with _error_ in overridden function

[yebblies]

When there is an error in the parameter types, default arguments or return type, propagate the error to the function's type.

http://d.puremagic.com/issues/show_bug.cgi?id=7462

[donc]

This was already in my pull. I actually entered the bug after I had a fix for it!
Sorry.

[donc]

Ah, interesting. This pull is primarily a fix for bug 7479. There's multiple issues, involved, since bug 7479 was a regression.

[yebblies]

Ah, I knew I'd seen a special-cased check for the return type being Type::terror somewhere, no wonder I couldn't find it in func.c.
Apart from 4269 I can't remember where I've run into this before, and I think there are/were also some issues with TypeSArray::semantic.

[yebblies]

Heh, it turns out this can cause crashes in several places because there are a bunch of assumptions that FuncDeclaration->type is always a TypeFunction.

[yebblies]

There are a lot of places in the code that assume FuncDeclaration::type is always a TypeFunction. Closing this until I can be sure it's fixed everywhere.