[core] WIP fix morph [GH #372]

pass the correct type info to pmc_reuse
allow the 2nd argument to be a Object PMC, so
use Parrot_pmc_reuse_init instead.

Define some FixedPMCArray morphs.

TODO:
- get_class Undef returns a PMCProxy object
- More basic arrays, Integer, String and Hash morphes
- non-builtin types via PARROT_CLASS(type)->id
  and Parrot_pmc_reuse_by_class

- morph old values into new type (pmc specific).
  e.g. *Array => Integer needs to assign the elements to the get_integer iv
morph: add morph methods to undef and fixedpmcarray

fixes the test to morph fixedpmcarray to integer
t/src/extend_vtable.t 9

t/pmc/undef.t: 10 still broken: String morph to Undef, get_class Undef is a PMCProxy
[test] start t/op/morph.t