They are rarely useful in my opinion.
This commit was mainly motivated by this message:
Video uses a non-standard and wasteful way to store B-frames ('packed B-frames'). Consider using a tool like VirtualDub or avidemux to fix it.
It's what's left over from the "Invalid and inefficient vfw-avi..."
warning that used to be printed when playing avi/divx files. Although
the new message is much better, it's still rather useless and poses
more questions than it answers. Besides, nobody wants to remux a file
when playing it, especially not if playback appears to be completely
fine. (There are some claims that these files raise CPU usage, but even
my old crappy CPU can decode low res avi/divx files at real time at
about x35 playback speed.)
core is used in many unix systems for core dumps. For that reason some tools
work under the assumption that the file is indeed a core dump (for example
autoconf does this).
This commit just renames the files. The following one will change all the
includes to fix compilation. This is done this way because git has a easier
time tracing file changes if there is a pure rename commit.