* Do a GC in mksnapshot to get rid of some extraneous junk.

* Do a GC in mksnapshot to get rid of some extraneous junk.
* Make snapshot more compact by coding the tag and the space
in one byte.  Contract some common sequences to one byte.
* Use back references only within one page.  Index from the
start of the space otherwise.
* Serialize Smis as raw data rather than int-encoding them.
This takes a little more space but is faster.
Review URL: http://codereview.chromium.org/341079

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3208 ce2b1a6d-e550-0410-aec6-3dcde31c8c00