[libpng16] Attempt to detect configuration issues with pngdeflate,

which requires both the correct libpng and the correct zlib to function
correctly.
[libpng16]Check ZLIB_VERNUM for mismatches, enclose #error in quotes
[libpng16] Renamed contrib/tools/fixitxt to contrib/tools/png-fix-itxt.

Added information in the documentation about problems with and fixes for
the bad CRC and bad iTXt chunk situations.
[libpng16] Renamed pnginflate to png-fix-too-far-back in contrib/tools.
[libpng16] Imported from libpng-1.6.3beta05.tar
[libpng16] Bump version to 1.6.3beta06
[libpng16] Cleaned up CHANGES and ANNOUNCE files.
[libng16] Fixed typo in png-fix-too-far-back "usage" output
[libpng16] Removed obsolete reference to "pnginflate" from ANNOUNCE
[libpng16] Revised contrib/pngminim/*/makefile to generate pnglibconf.h

with the right zlib headers.
[libpng16] Imported from libpng-1.6.3beta06.tar
[libpng16] Bump version to 1.6.3beta07