[vdr] Patch to Makefile so plugins are installed and man dirs are created

[Udo Richter]

C.Y.M wrote:
> How about we introduce LIBDIR and change the following line:
> 
> @cp $(PLUGINLIBDIR)/* $(BINDIR)/$(PLUGINLIBDIR)/
> 
> to
> 
> @cp $(PLUGINLIBDIR)/* $(LIBDIR)/

Too confusing. Plus, plugin makefiles do have a LIBDIR that can be
overruled by Make.config.

PLUGINLIBDIR is currently used only at two (!) places:
(1) make plugins-clean cleans that folder
(2) Via -DPLUGINDIR and #define DEFAULTPLUGINDIR, this is the default
for the -L parameter.

As explained, the use for plugins-clean is imho wrong, so this is
currently only a bad way to set the default path. Using this also as the
install destination sounds good to me.

Cheers,

Udo