Refine services description in Info.plist

This splits the service offerings in two: One for files, one for text selections. The use of NSSendFileTypes limits the service to only showing up in Finder for supported filetypes. The text selection service description is changed to match the description TextEdit uses for its "Open selection" service. Note that the file service is only compatible with 10.6+.
Enable auto-continuation of Markdown lists in instances where the bullet is not preceded by whitespace
Fix problem with undoing after hitting enter to eliminate auto-inserted list bullet

The deletion of the bullet + whitespace character wasn't going through the proper channels, and wasn't getting registered with the undo manager. Undoing after doing that would, rather than re-insert the bullet, delete some of the adjacent characters.
Fix exception when using Mountain Lion's press-and-hold to insert a special character

Specifically, when you hit a number key (from the pop-up menu) to select which special character. I suspect this causes a nil character to be inserted, or something like that; regardless, and an exception from trying to call a non-existent isEqualToString on it was the result. Switching around the literals and the parameter is a MUCH safer approach, and fixes this exception.
Merge branch 'list-continuation'
Merge branch 'services-fix'