On 32-bit platforms any pointer with 0 as LSB can be wrapped into Smi.  However, on 64-bit
platforms it's currently not the case as x64 Smis must have 0s in lower 32 bit word.
Even worse, macroassembler Move instruction will try to fetch integer value from Smi
and will shift by 32 bits to the right rendering stored pointer incorrect.

BUG=v8:1037

Review URL: http://codereview.chromium.org/6119009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6301 ce2b1a6d-e550-0410-aec6-3dcde31c8c00