add -include iostream when building tests so debug prints can easily be put in anytime

wscript

@@ -52,6 +52,6 @@ def build(bld):
         includes = test_includes,
         defines = test_defines,
         lib = test_libs,
-        cxxflags = ["-Wall", "-std=gnu++14", "--coverage", "-Wno-switch"],
+        cxxflags = ["-Wall", "-std=gnu++14", "--coverage", "-Wno-switch", "-include", "iostream"],
         linkflags = ["--coverage"],
         uselib = ["SDL2", "FreeType2"])