The zipdir tool now writes a fixed date and time for zip entries to make its output more deterministic.

Authentication errors, as of 98447d6e9903, will now show zandronum.pk3 if it is different between the client and server. However, this will often happen incorrectly, as the file can be different despite the actual protected content within being the same: zipdir writes the modification date and time of each file into the zip, which may differ between builds of same version, typically reflecting when the files in the zip were affected by a hg update. This MR prevents that by making the tool write a fixed value for the date and time of entries in the zip.

I chose 10 Dec 1993 as the date value, because it's obvious it's not the actual date, and being Doom's release date it's a little easter egg for anyone who decides to open the files in an archive manager. (I actually spent like an hour trying to figure the exact time Doom was uploaded to FTP, to no avail... so midnight it is for the time) Other suggestions for the date and time value are welcome :)