Change version numbers to 1.2.5.2 and release dates

Also added "-motley" to ZLIB_VERSION in zlib.h, so that versions
in-between 1.2.5.1 and 1.2.5.2 that are pulled down from github
can be identified as such if bugs are reported on them.

contrib/delphi/ZLib.pas

@@ -152,7 +152,7 @@ procedure DecompressToUserBuf(const InBuf: Pointer; InBytes: Integer;
   const OutBuf: Pointer; BufSize: Integer);
 
 const
-  zlib_version = '1.2.5.1';
+  zlib_version = '1.2.5.2';
 
 type
   EZlibError = class(Exception);