investigate replacing visit glue with debug info

[thestinger]

It seems like we could teach the type visitor to walk the debug info, instead of using visit glue. I don't know if this is a worthwhile idea, but it does seem feasible... It depends on how lossy the debugging information is.

[huonw]

We're currently experimenting with using the Show trait via #[deriving(Show)], rather than the reflection compiler magic.

Using DWARF still seem interesting for debugging printing, e.g. for printing information about things that have no usual method for printing.

[thestinger]

Reflection has been removed.