Add includes to headers to allow them to stand alone.

This allows compilers that can do header stand alone header parsing
to process libtiff.

libtiff/tif_dir.h

@@ -24,6 +24,10 @@
 
 #ifndef _TIFFDIR_
 #define	_TIFFDIR_
+
+#include "tiff.h"
+#include "tiffio.h"
+
 /*
  * ``Library-private'' Directory-related Definitions.
  */

libtiff/tif_predict.h

@@ -24,6 +24,10 @@
 
 #ifndef _TIFFPREDICT_
 #define	_TIFFPREDICT_
+
+#include "tiff.h"
+#include "tiffio.h"
+
 /*
  * ``Library-private'' Support for the Predictor Tag
  */

libtiff/tiffio.hxx

@@ -31,6 +31,7 @@
 
 #include <iostream>
 #include "tiff.h"
+#include "tiffio.h"
 
 extern TIFF* TIFFStreamOpen(const char*, std::ostream *);
 extern TIFF* TIFFStreamOpen(const char*, std::istream *);