one more try for ubuntu

src/Makevars

@@ -1,3 +1,3 @@
-PKG_CXXFLAGS=-I/usr/local/include -I/usr/include -I/opt/include -I/usr/include/tidy -I/usr/local/include/tidy
-PKG_CPPFLAGS=-I/usr/local/include -I/usr/include -I/opt/include -I/usr/include/tidy -I/usr/local/include/tidy
+#PKG_CXXFLAGS=-I/usr/local/include -I/usr/include -I/opt/include -I/usr/include/tidy -I/usr/local/include/tidy
+#PKG_CPPFLAGS=-I/usr/local/include -I/usr/include -I/opt/include -I/usr/include/tidy -I/usr/local/include/tidy
 PKG_LIBS=-ltidy

src/htmltidy.cpp

@@ -1,6 +1,14 @@
 #include <Rcpp.h>
+
+#ifdef __linux__
+#include <tidy/tidy.h>
+#include <tidy/buffio.h>
+#endif
+
+#ifdef __APPLE__
 #include <tidy.h>
 #include <tidybuffio.h>
+#endif
 
 // libtidy docs:
 // http://api.html-tidy.org/tidy/tidylib_api_5.2.0/tidyenum_8h.html#a3a1401652599150188a168dade7dc150