[libpng17] Bump version to 1.7.0beta56

ANNOUNCE

@@ -1,5 +1,5 @@
 
-Libpng 1.7.0beta55 - March 9, 2015
+Libpng 1.7.0beta56 - March 9, 2015
 
 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.
@@ -9,20 +9,20 @@ Files available for download:
 Source files with LF line endings (for Unix/Linux) and with a
 "configure" script
 
-   1.7.0beta55.tar.xz (LZMA-compressed, recommended)
-   1.7.0beta55.tar.gz
+   1.7.0beta56.tar.xz (LZMA-compressed, recommended)
+   1.7.0beta56.tar.gz
 
 Source files with CRLF line endings (for Windows), without the
 "configure" script
 
-   lp170b55.7z  (LZMA-compressed, recommended)
-   lp170b55.zip
+   lp170b56.7z  (LZMA-compressed, recommended)
+   lp170b56.zip
 
 Other information:
 
-   1.7.0beta55-README.txt
-   1.7.0beta55-LICENSE.txt
-   libpng-1.7.0beta55-*.asc (armored detached GPG signatures)
+   1.7.0beta56-README.txt
+   1.7.0beta56-LICENSE.txt
+   libpng-1.7.0beta56-*.asc (armored detached GPG signatures)
 
 Changes since the last public release (1.6.0):
 
@@ -746,6 +746,8 @@ Version 1.7.0beta55 [March 9, 2015]
   Added more error reporting in png_default_read_data().
   Merged png_free_data() with libpng-1.6.17rc02.
 
+Version 1.7.0beta56 [March 9, 2015]
+
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