(bug 26716, well partially anyways. kind of second half of r80608) Add a comment...

(bug 26716, well partially anyways. kind of second half of r80608) Add a comment to external editor ini control file explaining
what it is. This will give people who accidently select the preference a fighting chance to debug what is going on.

Of course, since it has a mime type of application/x-external-edit (or something like that), and the download would have
a .php extension, the chance they will open it in a text editor is pretty slim...

See bug 2760 for proposal to just kill the preference altogether.