MIPS: Do the qNaN fixup at de-serialization time.  This is a commit of https://chromiumcodereview.appspot.com/10093007/ for Paul Lind

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11405 ce2b1a6d-e550-0410-aec6-3dcde31c8c00