update the INSTALL_RPATH at the beginning instead of setting a new one, allows...

update the INSTALL_RPATH at the beginning instead of setting a new one, allows to give additional paths by hand

CMakeLists.txt

@@ -87,7 +87,7 @@ if (MORSE_DISTRIB_DIR OR EXISTS "${CMAKE_SOURCE_DIR}/cmake_modules/")
     set(CMAKE_BUILD_WITH_INSTALL_RPATH FALSE)
 
     # the RPATH to be used when installing
-    set(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/lib")
+    set(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_RPATH} ${CMAKE_INSTALL_PREFIX}/lib")
 
     # Misc options
     # ------------