Bug 6874: Force user to select a directory

Bug 6874: Force user to select a directory

This patch adds a javascript and a server-side checks

Test plan:
1/ Choose a file, leave the radios not selected and submit
2/ You have a javascript alert which prevents form to be submitted
3/ Disable javascript and repeat step 1
4/ Form is submitted but form is redisplayed with an error message
telling you to choose a directory.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>