Typedefs that resolve to slices are not recorded in DWARF as typedefs
but instead as structs in a way that there is no way to know they
are really slices using debug/dwarf.
Using golang.org/x/debug/dwarf instead this problem is solved and
as a bonus some types are printed with a nicer names: (struct string
→ string, struct []int → []int, etc)
Fixes#356 and #293
Use godeps to vendor dependencies and the normal go toolchain, with
GO15VENDOREXPERIMENT=1 set to properly vendor dependencies for reproducible
builds.