Cannot add file association edit area action

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Go to the Admin panel
2. Click the "File association" tab
3. Enter a file extension in the "Extension(s)" field
4. Choose the "edit_area" from the "Plugin" field
5. Double click file with file extension
6. Right click and choose edit from the context menu

What is the expected output? What do you see instead?
Expected output: The "Edit area" to open with the contents of the selected file 
loaded.

What I see instead: Nothing happens.

What version of the product are you using? On what operating system?
KFM version 1.4.6
Ubuntu 11.04 (GNU/Linux 2.6.32-042stab037.1 i686)
Apache/2.2.17 (Ubuntu)
PHP 5.3.5-1ubuntu7.3
Firefox 10.0.2
Google Chrome 17.0.963.56 m

Please provide any additional information below.
The file type I've tried to add is YAML(extension "yml"(I also tried the 
extension ".yml")). I also noticed that it said "unknown/mimetype" if you read 
the file information on a YAML-file, so I tried to add it to known mimetypes 
within apache in /etc/mime.types as "application/x-yaml". Apache now knows the 
file type and sends the correct headers, but I still can't edit the file in KFM.

Original issue reported on code.google.com by to...@froghouse.se on 23 Feb 2012 at 2:42

[GoogleCodeExporter]

I added the mimetype to classes/Mimtype.php and that fixed the error that with 
the mimtype displayed in the file info.

No progress on opening the file in edit area yet though.

Original comment by to...@froghouse.se on 23 Feb 2012 at 3:36