Add a fast case for one-element arrays in ArrayJoin

This case handles all one-element arrays that were not handled by _FastOneByteArrayJoin

BUG=
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/607503004

Patch from Fadi Meawad <fmeawad@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24334 ce2b1a6d-e550-0410-aec6-3dcde31c8c00