1. Separating out the instance-type check from the array-length operation.

2. I also changed the bounds-check on keyed loads to use the length property
for JS arrays (like we do for array stores).

The new pattern should use less registers and allow more checks to be eliminated.

Review URL: http://codereview.chromium.org/5961016

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6125 ce2b1a6d-e550-0410-aec6-3dcde31c8c00