[master] Change some instances of PNG_READ_UNKNOWN_CHUNKS_SUPPORTED

to PNG_HANDLE_AS_UNKNOWN to make it possible to build a libpng that can
use the png_set_keep_unknown_chunks() mechanism to ignore unused chunks
without having to save unknown chunks.

ANNOUNCE

@@ -1,5 +1,5 @@
 
-Libpng 1.2.38beta01 - June 5, 2009
+Libpng 1.2.38beta01 - June 12, 2009
 
 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.
@@ -69,20 +69,26 @@ version 1.2.37rc01 [May 27, 2009]
   No changes.
 
 versions 1.2.37 and 1.0.45 [June 4, 2009]
-  Reformatted several remaining "else statement;" and "if () statment;" into
+  Reformatted several remaining "else statement;" and "if () statement;" into
     two lines.
   Added "#define PNG_NO_WRITE_SWAP" to contrib/pngminim/encoder/pngusr.h
     and "define PNG_NO_READ_SWAP" to decoder/pngusr.h and preader/pngusr.h
   Added sections about the git repository and our coding style to the
     documentation (merged from libpng-1.4.0beta62)
-  Added a section about using png_get_io_ptr() in configure scripts to detect
-    the presence of libpng.
+  Added a section in the documentation about using png_get_io_ptr() in
+    configure scripts to detect the presence of libpng.
 
-versions 1.2.38 [June 5, 2009]
+version 1.2.38beta01 [June 12, 2009]
+  Revised libpng*.txt and libpng.3 to mention calling png_set_IHDR()
+    multiple times and to specify the sample order in the tRNS chunk,
+    because the ISO PNG specification has a typo in the tRNS table.
+  Changed several PNG_UNKNOWN_CHUNK_SUPPORTED to
+    PNG_HANDLE_AS_UNKNOWN_SUPPORTED, to make the png_set_keep mechanism
+    available for ignoring known chunks even when not saving unknown chunks.
 
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