the source code can be downloaded either via svn (https://pure-data.svn.sourceforge.net/svnroot/pure-data/trunk/externals/plug...) or as a tarball from: http://pure-data.svn.sourceforge.net/viewvc/pure-data/trunk/externals/plugin...
the build-system is scons based ("apt-get install scons"; and then run "scons" in the directory)
I downloaded the src from the svn installed scons (thanks for mentioning this!) and compiled the plugin~ external with no errors
some cursory observations using test patches I built yesterday -->
error: plugin~: no method for 'print'
plugin~: Warning: Plug-in defines activate() method but no deactivate() method
crash immediately