fixed bug in cmake file for the tutorial that was inhibiting debug mode

Former-commit-id: 2f97e9e4cb50b6ec9f6f1ff9f5d7e267ac5057ad

tutorial/CMakeLists.shared

@@ -65,8 +65,11 @@ link_directories(
 
 # Disable deprecated opengl code from libigl
 add_definitions(-DIGL_OPENGL_4)
-add_definitions(-DNDEBUG)
-add_definitions(-O3)
+
+IF(CMAKE_BUILD_TYPE MATCHES RELEASE)
+    add_definitions(-DNDEBUG)
+ENDIF(CMAKE_BUILD_TYPE MATCHES RELEASE)
+
 #add_definitions(-DENABLE_XML_SERIALIZATION)