code editor can not open files with arbitrary extension

it should be possible to open any file with the codeeditor. If it is not directly linked in the file-browser its ok (there a new menu entry “open with” should be added. But if you open a file using the “open file” dialog in the code editor any file should be opened.

(from redmine: issue id 1830, created on 2014-08-20 by Christian.Glaser, closed on 2014-08-21)