Fix SmiCompare on 64 bit to distinguish between comparisons where

Fix SmiCompare on 64 bit to distinguish between comparisons where
we know that both sides are Smi and those where we don't.  Fix inlined
symbol table probes to cope with strings, undefined and null (indicating
a deleted entry).  Some changes to other architectures that were found
with the new asserts.
Review URL: http://codereview.chromium.org/6682026

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7172 ce2b1a6d-e550-0410-aec6-3dcde31c8c00