(bug 40889) Fix XHTML in Special:Upload form labels

(bug 40889) Fix XHTML in Special:Upload form labels

We were using an improper method for adding labels to the form, namely
using something other than the ID (and in fact, a nonexistent ID) in the
'for' attribute. This patch uses the ID of the parent element and should
fix the issue.

Note: Upstream bug in Firefox prevents testing this patch in that browser.
Use Chromium, as the FF bug report says that it works there. See
https://bugzilla.mozilla.org/show_bug.cgi?id=701353 for more.

Change-Id: I19e06a3b94f67f364d129cbef4ecc232f108e82d