Fix some issues in the entity and subscript code
* lisp/org-macs.el (org-rm-props): Add org-emphasis to the properties
that must be removed.
* lisp/org.el (org-do-emphasis-faces): Add org-emphasis property to
items that have emphasis done wit font-lock.
(org-fontify-entities): Do not do anything in commented lines.
(org-unfontify-region): Decompose the region as well, because we do
composition during font-lock.
(org-raise-scripts): Do nothing inside an emphasis string.
Reported by Eric Fraga in http://article.gmane.org/gmane.emacs.orgmode/25940