[libpng16]Check ZLIB_VERNUM for mismatches, enclose #error in quotes

ANNOUNCE

@@ -71,6 +71,7 @@ Version 1.6.3beta05 [May 8, 2013]
       invalid values.
   Attempt to detect configuration issues with pngdeflate, which requires
     both the correct libpng and the correct zlib to function correctly.
+  Check ZLIB_VERNUM for mismatches, enclose #error in quotes
 
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CHANGES

@@ -4554,6 +4554,7 @@ Version 1.6.3beta05 [May 8, 2013]
       invalid values.
   Attempt to detect configuration issues with pngdeflate, which requires
     both the correct libpng and the correct zlib to function correctly.
+  Check ZLIB_VERNUM for mismatches, enclose #error in quotes
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit

contrib/tools/pngdeflate.c

@@ -26,14 +26,14 @@
 #endif
 
 #if PNG_LIBPNG_VER < 10603 /* 1.6.3 */
-#  error pngdeflate will not work with libpng versions prior to 1.6.3
+#  error "pngdeflate will not work with libpng versions prior to 1.6.3"
 #endif
 
 #ifdef PNG_READ_SUPPORTED
 #include <zlib.h>
 
 #ifndef PNG_MAXIMUM_INFLATE_WINDOW
-#  error pngdeflate not supported in this libpng version
+#  error "pngdeflate not supported in this libpng version"
 #endif
 
 #if PNG_ZLIB_VERNUM >= 0x1240

pngpriv.h

@@ -694,6 +694,24 @@
 #include "pngstruct.h"
 #include "pnginfo.h"
 
+/* Validate the include paths - the include path used to generate pnglibconf.h
+ * must match that used in the build, or we must be using pnglibconf.h.prebuilt:
+ */
+#if PNG_ZLIB_VERNUM != 0 && PNG_ZLIB_VERNUM != ZLIB_VERNUM
+#  error ZLIB_VERNUM != PNG_ZLIB_VERNUM \
+      "-I (include path) error: see the notes in pngpriv.h"
+   /* This means that when pnglibconf.h was built the copy of zlib.h that it
+    * used is not the same as the one being used here.  Because the build of
+    * libpng makes decisions to use inflateInit2 and inflateReset2 based on the
+    * zlib version number and because this affects handling of certain broken
+    * PNG files the -I directives must match.
+    *
+    * The most likely explanation is that you passed a -I in CFLAGS, this will
+    * not work; all the preprocessor directories and in particular all the -I
+    * directives must be in CPPFLAGS.
+    */
+#endif
+
 /* This is used for 16 bit gamma tables -- only the top level pointers are
  * const; this could be changed:
  */