[libpng16] Use "FALL THROUGH" comment consistently in switch statements.

pngerror.c

@@ -163,7 +163,7 @@ png_format_number(png_const_charp start, png_charp end, int format,
          case PNG_NUMBER_FORMAT_02u:
             /* Expects at least 2 digits. */
             mincount = 2;
-            /* fall through */
+            /* FALL THROUGH */
 
          case PNG_NUMBER_FORMAT_u:
             *--end = digits[number % 10];
@@ -173,7 +173,7 @@ png_format_number(png_const_charp start, png_charp end, int format,
          case PNG_NUMBER_FORMAT_02x:
             /* This format expects at least two digits */
             mincount = 2;
-            /* fall through */
+            /* FALL THROUGH */
 
          case PNG_NUMBER_FORMAT_x:
             *--end = digits[number & 0xf];

pngrtran.c

@@ -1245,7 +1245,7 @@ png_init_rgb_transformations(png_structrp png_ptr)
             default:
 
             case 8:
-               /* Already 8 bits, fall through */
+               /* FALL THROUGH (Already 8 bits) */
 
             case 16:
                /* Already a full 16 bits */

pngwrite.c

@@ -937,7 +937,7 @@ png_set_filter(png_structrp png_ptr, int method, int filters)
          case 5:
          case 6:
          case 7: png_app_error(png_ptr, "Unknown row filter for method 0");
-            /* Fall through */
+            /* FALL THROUGH */
 #endif /* PNG_WRITE_FILTER_SUPPORTED */
          case PNG_FILTER_VALUE_NONE:
             png_ptr->do_filter = PNG_FILTER_NONE; break;