Fix #171

* js2-mode.el (js2-parse-primary-expr): Use
`js2-current-token-end' to retrieve the end of the current token.
This works better if parsing errored on EOF.
(js2-read-regexp): Don't try to set `syntax-table' property (it
didn't work anyway, `syntax-class' is bogus).
js2-parse-primary-expr: Make some vars "more" local