[REG 3.3->3.4] mimetypes that inherit application/x-executable are opened in binary editor even if they also inherit text/plain

Open dumper.py for example.

The mime hierarchy is:

• text/x-python
  • application/x-executable
    • application/octet-stream
  • text/plain

Since the recursion is DFS, application/octet-stream, which is associated with the binary editor, is matched first.

Same goes for application/x-ruby.