* lisp/progmodes/ruby-mode.el (ruby-syntax-expansion-allowed-p): New

* lisp/progmodes/ruby-mode.el (ruby-syntax-expansion-allowed-p): New
function, checks if expression expansion is allowed in given parse
state.
(ruby-syntax-propertize-expansion): Use it.
(ruby-syntax-propertize-function): Bind `case-fold-search' to nil
around the body.

* test/automated/ruby-mode-tests.el: New tests, for percent literals
and expression expansion.