fixes in libdl/DL cmake

minor tweaks in pybullet OpenAI gym locomotion envs (connect to shared memory before going GUI/DIRECT)
bump up pybullet version to 1.3.6

CMakeLists.txt

@@ -39,7 +39,7 @@ ENDIF (BULLET2_USE_THREAD_LOCKS)
 
 
 IF(NOT WIN32)
-	SET(DL dl)
+	SET(DL ${CMAKE_DL_LIBS})
 	IF(CMAKE_SYSTEM_NAME MATCHES "Linux")
 		MESSAGE("Linux")
 		SET(OSDEF -D_LINUX)
@@ -50,7 +50,6 @@ IF(NOT WIN32)
 		ELSE(APPLE)
 			MESSAGE("BSD?")
 			SET(OSDEF -D_BSD)
-			SET(DL "")
 		ENDIF(APPLE)
 	ENDIF(CMAKE_SYSTEM_NAME MATCHES "Linux")
 ENDIF(NOT WIN32)