opening unknown file types in external applications

[John W. Eaton]

The following change allows a double click on a data file in the file
browser to load the file into the Octave workspace instead of opening
it in the editor.

  http://hg.savannah.gnu.org/hgweb/octave/rev/04fb96f4bea1

All other files are still opened in the editor.  That's great for text
files, but not so good for PDF files.

What I'd like to do now is recognize text files and open them in the
editor, but ask the OS or desktop environment to open all other files
in an appropriate external application.  Is there some more or less
standard way of doing that?

jwe