Fixed bug where regexps were not callable across contexts since the
callable test used object identity on the regexp constructor.  Changed
typeof RegExp from 'object' to 'function' for compatibility.

Review URL: http://codereview.chromium.org/171039


git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2696 ce2b1a6d-e550-0410-aec6-3dcde31c8c00