Use cl-incf instead of cl

* yasnippet.el (yas--snippet-next-id, yas--real-line-beginning):
Use `cl-incf'.
Merge pull request #519 from syohex/use-cl-macro
Signal an error on recursive yas--fallback calls

* yasnippet.el (yas--fallback): let-bind yas-fallback-behavior to
  'yas--fallback before actually doing the fallback. Signal an error if
  it's 'yas--fallback (indicating we're in an infinte loop).
Merge pull request #524 from npostavs/fallback-loop

Signal an error on recursive yas--fallback calls
Closes #525, closes #526: Prevent some keybinding fallback loops

* yasnippet.el (yas--keybinding-beyond-yasnippet): Add docstring.
(yas--fallback): Also let-bind `yas-minor-mode' to nil when
falling back.
Closes #527: Unbreak case where yas-fallback-behaviour is a list

* yasnippet.el (yas--fallback): Extract interesting values from
`yas-fallback-behaviour' before rebinding.
Tweak README.mdown to simplify bug reporting paragraph
Update README.mdown
Update snippets submodule