[libpng17] Moved READ_GAMMA to pngrtran.c. This makes everything in pngrtrans.c

depend on READ_TRANSFORMS and moves all the transform gamma (READ_GAMMA)
code from elsewhere to png_tran.c.  There are no code changes.
There is one remaining use of the gamma (16-bit) code in the simplified
API in pngread.c but that is because of a long-standing libpng bug,
namely that the gamma corrected palette is no produced by
png_read_update_info (John Bowler).

ANNOUNCE

@@ -1,5 +1,5 @@
 
-Libpng 1.7.0beta63 - June 4, 2015
+Libpng 1.7.0beta63 - June 5, 2015
 
 This is not intended to be a public release.  It will be replaced
 within a few weeks by a public version or by another test version.
@@ -814,13 +814,20 @@ Version 1.7.0beta62 [June 1, 2015]
     far as we can tell, no one uses it. The png_set_filter_heuristics() and
     png_set_filter_heuristics_fixed() APIs are retained but deprecated.
 
-Version 1.7.0beta63 [June 4, 2015]
+Version 1.7.0beta63 [June 5, 2015]
   Quieted Coverity issues in pngfix.c, png-fix-itxt.c, pngvalid.c,
     pngstest.c, and pngimage.c. Most seem harmless, but png-fix-itxt
     would only work with iTXt chunks with length 255 or less.
   Fixed cexcept.h in which GCC 5 reported that one of the auto
     variables in the Try macro needs to be volatile to prevent value
     being lost over the setjmp, and fixed g++ build breaks (John Bowler).
+  Moved READ_GAMMA to pngrtran.c. This makes everything in pngrtrans.c
+    depend on READ_TRANSFORMS and moves all the transform gamma (READ_GAMMA)
+    code from elsewhere to png_tran.c.  There are no code changes. 
+    There is one remaining use of the gamma (16-bit) code in the simplified
+    API in pngread.c but that is because of a long-standing libpng bug,
+    namely that the gamma corrected palette is no produced by
+    png_read_update_info (John Bowler).
 
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