Fixed type qualification
Fixed another Lazy.Undefined on Core
Type qualification is actually quite annoying in the general case

disabling it by default, we can check the cases where it's useful after or add an option.
For example, 'Core_kernel.Std_kernel.Int.t -> Core_kernel.Std_kernel.Int.t -> Core_kernel.Std_kernel.Int.t' is
not really better than 't -> t -> t' for Core.Std.Int./
Experimental: load positions of idents through shadowed module aliasing

This allows, for example, to jump to the definition of LibIndex.Misc.unique_subdir, while
we would previously only get the shadowing signature from libIndex.mli

It should be made so that loading the cmt isn't done once for every position looked up though
(not a problem atm since we usually just query one loc).

Only works on >4.02, obviously.