[truetype] Recalculate the sfnt table checksum always.

* src/truetype/ttobjs.c (tt_get_sfnt_checksum): Recalculate
the sfnt table checksum even if non-zero value is writte in
the TrueType font header.  Some bad PDF generators write
wrong values.  For detail, see examples and benchmark tests
of the latency by recalculation:
http://lists.gnu.org/archive/html/freetype-devel/2011-04/msg00091.html
http://lists.gnu.org/archive/html/freetype-devel/2011-04/msg00096.html

ChangeLog

@@ -1,3 +1,15 @@
+2011-04-30  suzuki toshiya  <mpsuzuki@hiroshima-u.ac.jp>
+
+	[truetype] Recalculate the sfnt table checksum always.
+
+	* src/truetype/ttobjs.c (tt_get_sfnt_checksum): Recalculate
+	the sfnt table checksum even if non-zero value is writte in
+	the TrueType font header.  Some bad PDF generators write
+	wrong values.  For detail, see examples and benchmark tests
+	of the latency by recalculation:
+	http://lists.gnu.org/archive/html/freetype-devel/2011-04/msg00091.html
+	http://lists.gnu.org/archive/html/freetype-devel/2011-04/msg00096.html
+
 2011-04-30  suzuki toshiya  <mpsuzuki@hiroshima-u.ac.jp>
 
 	[truetype] Register a set of tricky fonts, NEC FA family.

src/truetype/ttobjs.c

@@ -213,8 +213,10 @@
   tt_get_sfnt_checksum( TT_Face    face,
                         FT_UShort  i )
   {
+#if 0 /* if we believe the written value, use following part. */
     if ( face->dir_tables[i].CheckSum )
       return face->dir_tables[i].CheckSum;
+#endif
 
     if ( !face->goto_table )
       return 0;