add syntax cIncludeDir "$projpath/include"; do not use recursive search paths; add test tests/tnimterop_cpp.nim

tests/include/test2.cpp

@@ -0,0 +1,8 @@
+#include "test2.hpp"
+
+// BUG: should complain
+// # include test2.h
+
+int test_call_int() {
+  return 5; 
+}