Allow 'give up on this function scope, continue with next' errors in typeck

[marijnh]

Currently, when the check phase comes across something it really can't type, it bails out entirely and aborts the compilation. It should not be too hard to set it up to continue typechecking other function blocks, since those are mostly separate units. (Of course, getting a function declaration wrong might result in multiple errors with the same cause, but that still seems preferable to having the compile give up completely.)

[catamorphism]

I think that with my work on #1871, this is no longer an issue.