Upgrade libjpeg 8c -> 9e

extern/libjpeg/jfdctfst.c

@@ -2,7 +2,7 @@
  * jfdctfst.c
  *
  * Copyright (C) 1994-1996, Thomas G. Lane.
- * Modified 2003-2009 by Guido Vollbeding.
+ * Modified 2003-2017 by Guido Vollbeding.
  * This file is part of the Independent JPEG Group's software.
  * For conditions of distribution and use, see the accompanying README file.
  *
@@ -44,7 +44,7 @@
  */
 
 #if DCTSIZE != 8
-  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
+  Sorry, this code only copes with 8x8 DCT blocks. /* deliberate syntax err */
 #endif
 
 
@@ -109,6 +109,8 @@
 
 /*
  * Perform the forward DCT on one block of samples.
+ *
+ * cK represents cos(K*pi/16).
  */
 
 GLOBAL(void)
@@ -145,7 +147,7 @@ jpeg_fdct_ifast (DCTELEM * data, JSAMPARRAY sample_data, JDIMENSION start_col)
     tmp11 = tmp1 + tmp2;
     tmp12 = tmp1 - tmp2;
 
-    /* Apply unsigned->signed conversion */
+    /* Apply unsigned->signed conversion. */
     dataptr[0] = tmp10 + tmp11 - 8 * CENTERJSAMPLE; /* phase 3 */
     dataptr[4] = tmp10 - tmp11;