allow to install the plugind to the same place as the pkconfig files

cmake @ a831f540

-Subproject commit 14fd3668f967ea742f247054896f253d62438950
+Subproject commit a831f5403a93b67c6cb8675625e79dd676a565f3

src/CMakeLists.txt

@@ -110,7 +110,7 @@ FOREACH(LIBRARY_NAME ${plugins})
   PKG_CONFIG_USE_DEPENDENCY(${LIBRARY_NAME} pinocchio)
   PKG_CONFIG_USE_DEPENDENCY(${LIBRARY_NAME} sot-core)
 
-  INSTALL(TARGETS ${LIBRARY_NAME} DESTINATION ${DYNAMIC_GRAPH_PLUGINDIR})
+  INSTALL(TARGETS ${LIBRARY_NAME} DESTINATION ${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}/plugin)
 
   # --- PY ---
   STRING(REPLACE - _ PYTHON_LIBRARY_NAME ${LIBRARY_NAME})