Multiple dispatch branch merged

[Allison Randal]

I've merged the multiple dispatch branch (pdd27mmd) into trunk. All core 
tests pass for me on Mac OS 10.5.5 (Intel) and Ubuntu 6.10 (32 bit).

One apparently unrelated failure on Ubuntu 8.04 (64 bit) (a test for 
word size in t/native_pbc/header.t).

A few known failures in Rakudo that are being worked on.

Please report any failures on other platforms/operating systems.

Allison