added excerpts correction

Octopress allows adding "<!-- more -->" (excerpt tag) in the post to show only its first section. Adding it to org file and exporting results in conversion to character entities (like ``&lt;!&ndash; more &ndash;&gt;``). In that form excerpts are no longer recognized, so they cannot be converted to proper links in future processing.

I added code, which searches for excerpts coded with character entities and replaces them back with regular text html comments. Is this a good idea to merge it into master or should I rather implement my own "org-export-octopress-final-hook"?