When double-clicking files that have the +x bit and can be executed you get a dialogue prompting you if you want to execute, execute in terminal or view the file. If you press view and the file has the content of what I'm going to provide it will be executed still.

You have to create an executable file with this content:
#!/bin/bash

for x in `find . -type f`; do new=`echo $x | tr '[A-Z]' '[a-z]'`; mv $x $new; done

Other files are opened with the default text editor, as they should be.

This bug was originally reported by yetanotherhandle in Ubuntu on Launchpad,  https://launchpad.net/bugs/364376