Fix bug 11558 updxlrator: use mirror mode for SHA1, filenames

Fix bug 11558 updxlrator: use mirror mode for SHA1, filenames

Most Microsoft updates now contain an SHA1 hash in the filename.
Since these files are uniquely identifiable, use mirror mode
(which creates a hash of just the filename instead of the entire URL)
to cache them. (But first check the URL cache to see if it
has been downloaded as a URL already.)

This is a HUGELY needed fix. Windows 10 updates are 5+ GB
per month, and we lose several days of bandwidth downloading
duplicates from different mirrors. Sometimes a single client
will request the same patch from multiple mirrors. That's bad.
This patch will save a ton of bandwidth, and lots of disk space.

The patch limits the SHA1 test to microsoft only, but it
could be easily expanded to other vendors if there is a need.

Signed-off-by: Justin Luth  <jluth@mail.com>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>