[registry] Should have clearer message when file is too large

[njx]

Currently, if you try to upload a ZIP file that's over our 5MB limit, the registry shows an "invalid ZIP file" error. We should show a real error, and probably also mention the limit somewhere on the page.

[njx]

Medium priority to me. We might just want to raise the limit to 10MB and then lower the priority.

[peterflynn]

See also #6060, which is about considering raising the limit

[peterflynn]

Reviewed - marking for 1.0 now that #6060 is on the back burner

[njx]

Reviewed - leaving on 1.0 list.

[njx]

@dangoor - punting this one to you.

[zaggino]

I have currently 0.4MB file which I cannot upload due to "Invalid zip file" but all the compressing software I tried (7zip, winzip, native ubuntu one) has no problems with it: http://www61.zippyshare.com/v/11279601/file.html