fixed CMAKE_MODULE_PATH overwriting previous values

CMakeLists.txt

@@ -168,7 +168,7 @@ include_directories(
     ${CMAKE_CURRENT_BINARY_DIR}/include
 )
 
-SET(CMAKE_MODULE_PATH       "${CMAKE_CURRENT_SOURCE_DIR}/cmake-modules" )
+LIST(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake-modules" )
 SET(LIBASSIMP_COMPONENT     "libassimp${ASSIMP_VERSION_MAJOR}.${ASSIMP_VERSION_MINOR}.${ASSIMP_VERSION_PATCH}" )
 SET(LIBASSIMP-DEV_COMPONENT "libassimp${ASSIMP_VERSION_MAJOR}.${ASSIMP_VERSION_MINOR}.${ASSIMP_VERSION_PATCH}-dev" )
 SET(CPACK_COMPONENTS_ALL assimp-bin ${LIBASSIMP_COMPONENT} ${LIBASSIMP-DEV_COMPONENT} assimp-dev)