[devel] Freeze build-time only configuration in the build.

    In all prior versions of libpng most configuration options
    controlled by compiler #defines had to be repeated by the
    application code that used libpng.  This patch changes this
    so that compilation options that can only be changed at build
    time are frozen in the build.  Options that are compiler
    dependent (and those that are system dependent) are evaluated
    each time - pngconf.h holds these.  Options that can be changed
    per-file in the application are in png.h.  Frozen options are
    in the new installed header file pnglconf.h
diff --git a/CHANGES b/CHANGES
index 36a488e..1f04649 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2622,7 +2622,7 @@
   Combined multiple png_warning() calls for a single error.
   Restored the macro definition of png_check_sig().
 
-version 1.5.0beta17 [April 17, 2010]
+version 1.5.0beta17 [April 16, 2010]
   Added some "(long)" typecasts to printf calls in png_handle_cHRM().
   Documented the fact that png_set_dither() was disabled since libpng-1.4.0.
   Reenabled png_set_dither() but renamed it to png_set_quantize() to reflect
@@ -2630,6 +2630,16 @@
     the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros to
     PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS.
   Added some "(long)" typecasts to printf calls in png_handle_cHRM().
+  Freeze build-time only configuration in the build.
+    In all prior versions of libpng most configuration options
+    controlled by compiler #defines had to be repeated by the
+    application code that used libpng.  This patch changes this
+    so that compilation options that can only be changed at build
+    time are frozen in the build.  Options that are compiler
+    dependent (and those that are system dependent) are evaluated
+    each time - pngconf.h holds these.  Options that can be changed
+    per-file in the application are in png.h.  Frozen options are
+    in the new installed header file pnglconf.h
 
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