Add Fltk and Gettext include dirs when compiling tests

tests/CMakeLists.txt

@@ -1,3 +1,6 @@
+include_directories(${FLTK_INCLUDE_DIR})
+include_directories(${GETTEXT_INCLUDE_DIR})
+
 include_directories(${CMAKE_SOURCE_DIR}/common)
 
 add_library(test_util STATIC util.cxx)