Please add a tracker in the Joomla Feature Tracker on joomlacode ( http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemBrowse&tracker_id=8549 )
Also, this pull is so incomplete that it cannot be tested.

I've added some changes and options. It's working fine and in my opinion it's ready for a pull right now. Also added a tracker: http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=28565. Please advice.

Test instructions (J!2.5)

1- Overwrite your J2.5 files:
https://github.com/joomla/joomla-cms/pull/214/files
2- Go to article manager in back-end Joomla.
3- Options -> Integration -> JGLOBAL_FEED_SHOW_READMORE_LABEL: Show
4- Add some articles, split them with readmore. Create menu-item of type
category. Maybe you need to use the syndication module to get the RSS feed
link.
5- Go to your RSS feed for that category with Firefox:
view-source:http://your-rss-feed.com
6- Now you can see the read more links in the descriptions. You can turn them
off with step 3.

Corrected your patch. See joomlacode tracker. As I commented there, I see no use for the Read More.