Allocate new AccessorPairs with holes instead of undefined.

Allocate new AccessorPairs with holes instead of undefined.

This is essential for the upcoming map sharing with accessors, and we aleady
have enough machinery to handle the holes now. Furthermore, use "To" template in
2 nearby functions, and made naming a bit more consistent.

In a nutshell: This CL should have no visible effect at all at the moment.
Famous last words...

Review URL: https://chromiumcodereview.appspot.com/9594013

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10919 ce2b1a6d-e550-0410-aec6-3dcde31c8c00