[devel] Supply default values for PNG_USER_PRIVATEBUILD and PNG_USER_DLLFNAME_POSTFIX

in pngpriv.h in case the user forgot to define them in their pngusr.h.  This
means it is safe for people not building a DLL to omit these defines from pngusr.h.
diff --git a/CHANGES b/CHANGES
index 41adc8c..0052da1 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3014,7 +3014,7 @@
   Implemented progressive read in pngvalid.c gamma tests
   Turn on progressive reader in pngvalid.c by default and tidy code.
 
-Version 1.5.0beta45 [August 24, 2010]
+Version 1.5.0beta45 [August 25, 2010]
   Added an explicit make step to projects/vstudio for pnglibconf.h
     Also corrected zlib.vcxproj into which Visual Studio had introduced
     what it calls an "authoring error".  The change to make pnglibconf.h
@@ -3022,6 +3022,8 @@
     file from scripts/pnglibconf.dfa as the other build systems do.
   Changed pngvalid to work when floating point APIs are disabled
   Renamed the prebuilt scripts/pnglibconf.h to scripts/pnglibconf.h.prebuilt
+  Supply default values for PNG_USER_PRIVATEBUILD and PNG_USER_DLLFNAME_POSTFIX
+    in pngpriv.h in case the user forgot to define them in their pngusr.h
 
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