Merge several fixes from upsteam ruby-mode.

Merge several fixes from upsteam ruby-mode.

* lisp/progmodes/ruby-mode.el (ruby-here-doc-beg-match): Fix for
here-doc which ends with an underscore.
(ruby-mode-set-encoding): Skip shebang line always.
(ruby-mode-map): Bind C-c C-c to comment-region.
(ruby-expr-beg, ruby-font-lock-keywords): Highlight literal hash
key labels as symbols.
(ruby-forward-sexp): Stop after literal hash key labels.
(ruby-font-lock-syntactic-keywords): Highlight regexp after open
bracket.