Get Ruby's SMIE code to pass the test suite.

Get Ruby's SMIE code to pass the test suite.
* lisp/progmodes/ruby-mode.el (ruby-use-smie): Change default.
(ruby-comment-column): Follow the global default, by default.
(ruby-smie-grammar): Add assignment syntax.
(ruby-smie--implicit-semi-p): No implicit semi-colon after an
open-paren, a comma, or a \.
(ruby-smie--forward-token, ruby-smie--backward-token): Handle heredocs,
and line continuations.
(ruby-smie-rules): Adjust handling of open-paren, now that it's never
followed by implicit semi-colons.  Add rule for string concatenation
and for indentation at BOB.
(ruby-forward-sexp, ruby-backward-sexp): Adjust for when smie is in use.

* lisp/emacs-lisp/smie.el (smie-next-sexp): Don't go back to pos before
calling next-sexp, since next-token may have skipped chars which
next-sexp doesn't know should be skipped!

* test/indent/ruby.rb: Port a few cases from automated/ruby-mode-tests.el.
Adjust indentation of continued line to the new SMIE behavior.