Our 32 bit Windows installer currently installs some binaries (dll and
exe files) in the Windows system32 directory. This is unnecessary (all
required dlls are already in the program bin directory where pd.exe will
readily find them), and actually a nuisance, since we currently don't
remove some of the dlls in system32 again when uninstalling, causing a
lot of inconvenient prompts from the installer when upgrading or
reinstalling.

If the user wants to run cyclist, pdreceive, or pdsend from whatever
command line he uses, he can easily add the program bin directory to
PATH himself. That's much better than having our installer pollute the
system32 directory.

The mingw64 build already does it that way, here we simply apply the
same fixes to the mingw32 build.

The build directory needs to be cleaned out for a subsequent rebuild to work in the Darwin app build.

This commit adds initial packaging to build and distribute Purr Data
using Flatpak.

Add some comments and a few more useful desktop action examples to the main desktop file, so that the user understands how to adjust these if needed.

Replace pd-gui -> nw in the ForceQuit actions, which is the proper name of the GUI program on Linux.

These aren't going to be substituted in desktop actions anyway, because
desktop actions are supposed to be chosen from a menu, not being dragged to.

We do this to prevent extra arguments to be passed from the DE.

At least on KDE, it seems that the desktop file itself gets passed if the
action is invoked by right-clicking the icon on the desktop (this doesn't
happen with panel icons). Maybe this is a bug in KDE, but we need to prevent
this, because otherwise Purr Data tries to open the desktop file as a patch,
which of course will cause a bunch of ugly error messages in the main window.

Fix the Debian control files once again, since the dependency auto-detection needs a Depends line in there.

Make INCREMENTAL work on Windows (must be passed as make variable, as shell variable is not inherited in submakes).