[libpng17] Bump version to 1.7.0beta18

ANNOUNCE

@@ -1,5 +1,5 @@
 
-Libpng 1.7.0beta17 - August 22, 2013
+Libpng 1.7.0beta18 - August 22, 2013
 
 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.
@@ -9,19 +9,19 @@ Files available for download:
 Source files with LF line endings (for Unix/Linux) and with a
 "configure" script
 
-   1.7.0beta17.tar.xz (LZMA-compressed, recommended)
-   1.7.0beta17.tar.gz
+   1.7.0beta18.tar.xz (LZMA-compressed, recommended)
+   1.7.0beta18.tar.gz
 
 Source files with CRLF line endings (for Windows), without the
 "configure" script
 
-   lp170b17.7z  (LZMA-compressed, recommended)
-   lp170b17.zip
+   lp170b18.7z  (LZMA-compressed, recommended)
+   lp170b18.zip
 
 Other information:
 
-   1.7.0beta17-README.txt
-   1.7.0beta17-LICENSE.txt
+   1.7.0beta18-README.txt
+   1.7.0beta18-LICENSE.txt
    Gnupg/*.asc (PGP armored detached signatures)
 
 Changes since the last public release (1.6.0):
@@ -344,7 +344,7 @@ Version 1.7.0beta16 [July 5, 2013]
   Ported ARM no-read patch from libpng16.
   Ported pngfix.c patches from libpng16.
 
-Version 1.7.0beta17 [August 22, 2013]
+Version 1.7.0beta17 [August 21, 2013]
   Revised manual about changes in iTXt chunk handling made in libpng-1.6.0.
   Added "/* SAFE */" comments in pngrutil.c and pngrtran.c where warnings
     may be erroneously issued by code-checking applications.
@@ -352,6 +352,8 @@ Version 1.7.0beta17 [August 22, 2013]
   Delay calling png_init_filter_functions() until a row with nonzero filter
     is found.
 
+Version 1.7.0beta18 [August 22, 2013]
+
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