add a `duneactivate` script to `bin` that can be used instead of `activate` to

also set the `LD_LIBRARY_PATH`

[bugfix] used the wrong way to access the path to a sourced script - was working by chance

bin/CMakeLists.txt

@@ -3,6 +3,7 @@ install(PROGRAMS
   duneproject
   dunecontrol
   dunepackaging.py
+  duneactivate
   dune-git-whitespace-hook
   rmgenerated.py
   setup-dunepy.py

bin/duneactivate

+envpath=`dirname "${BASH_SOURCE[0]}"`
+source $envpath/activate
+export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$VIRTUAL_ENV/lib