rustc: Ignore the return value of native functions that return nil. stage1 can build libstd now, though it leaks.

NOTE: all 'long' parameters now use a double dash, so --shared, rather
than gcc-style -shared.

Kick ty_var and ty_local entries out of the type store. Pre-compute presence of var, local, param and bound_params in types.

rustc: Add a -save-temps option to save bitcode and write output simultaneously; document command line switches

rustc: Pass a "type context" around instead of directly passing the type store; prep for removing type annotations