Add PNG_SKIP_SETJMP_CHECK macro

ANNOUNCE

@@ -86,7 +86,9 @@ version 1.2.36beta04 [April 5, 2009]
   Fixed potential memory leak of "new_name" in png_write_iCCP() (Ralph Giles)
 
 version 1.2.36beta05 [April 13, 2009]
-  None.
+  Added "ifndef PNG_SKIP_SETJMP_CHECK" block in pngconf.h to allow
+    application code writers to bypass the check for multiple inclusion
+    of setjmp.h when they know that it is safe to ignore the situation.
 
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CHANGES

@@ -2353,7 +2353,10 @@ version 1.2.36beta04 [April 5, 2009]
   Fixed potential memory leak of "new_name" in png_write_iCCP() (Ralph Giles)
 
 version 1.2.36beta05 [April 13, 2009]
-  None.
+  Added "ifndef PNG_SKIP_SETJMP_CHECK" block in pngconf.h to allow
+    application code writers to bypass the check for multiple inclusion
+    of setjmp.h when they know that it is safe to ignore the situation.
+  Made some cosmetic changes to whitespace in pngtest output.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
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pngconf.h

@@ -314,21 +314,29 @@
 #ifdef PNG_SETJMP_SUPPORTED
 /* This is an attempt to force a single setjmp behaviour on Linux.  If
  * the X config stuff didn't define _BSD_SOURCE we wouldn't need this.
+ *
+ * You can bypass this test if you know that your application uses exactly
+ * the same setjmp.h that was included when libpng was built.  Only define
+ * PNG_SKIP_SETJMP_CHECK while building your application, prior to the
+ * application's '#include "png.h"'. Don't define PNG_SKIP_SETJMP_CHECK
+ * while building a separate libpng library for general use.
  */
 
-#  ifdef __linux__
-#    ifdef _BSD_SOURCE
-#      define PNG_SAVE_BSD_SOURCE
-#      undef _BSD_SOURCE
-#    endif
-#    ifdef _SETJMP_H
-     /* If you encounter a compiler error here, see the explanation
-      * near the end of INSTALL.
-      */
-         __pngconf.h__ already includes setjmp.h;
-         __dont__ include it again.;
-#    endif
-#  endif /* __linux__ */
+#  ifndef PNG_SKIP_SETJMP_CHECK
+#    ifdef __linux__
+#      ifdef _BSD_SOURCE
+#        define PNG_SAVE_BSD_SOURCE
+#        undef _BSD_SOURCE
+#      endif
+#      ifdef _SETJMP_H
+       /* If you encounter a compiler error here, see the explanation
+        * near the end of INSTALL.
+        */
+           __pngconf.h__ in libpng already includes setjmp.h;
+           __dont__ include it again.;
+#      endif
+#    endif /* __linux__ */
+#  endif /* PNG_SKIP_SETJMP_CHECK */
 
    /* include setjmp.h for error handling */
 #  include <setjmp.h>