I am going to forbid plug-ins from being installed directly in the root
of the plug-ins/ directory. They will have to be installed in a
subdirectory named the same as the entry point binary.
This may seem useless for our core plug-ins which are nearly all
self-contained in single binaries, but this is actually a necessary
restriction to eliminate totally the DLL hell issue on Windows. Moving
core plug-ins in subfolders is only a necessary consequence for it.
(cherry picked from commit 870ca6334d)
