The repository has moved here, but there the old repo remains, unsyced, and with no warning

Since x264 moved to this new repository, git://git.videolan.org/x264.git still works, but is no longer synced.

This is both good (don't break scripts), and also very problematic: Nobody is going to know to switch to this repository if they don't follow the mailing list (very few users do). configure should be modified to output a loud warning if it is detected that the user is building from the old repository URL; this is what, for example, FFmpeg did when they moved git URLs.

I suspect a lot of the bugs I am catching lately, are due almost all users actually using the old repo URL, which doesn't get new commits, and thus no users are testing the new commits. This happened to us (Vimeo) too: we had scripts using the old URL that silently kept working, and we found several bugs when switching to the new URL. If it can happen to us, who have several developers active in the community, it can happen to everyone.