[libpng17] Changed ZlibSrcDir from 1.2.5 to 1.2.8 in projects/vstudio.
[libpng17] Moved configuration information from the manual to the INSTALL

file.
[libpng17] Imported from libpng-1.7.0beta34.tar
[libpng17] Bump version to 1.7.0beta35
[libpng17] Mention scripts/pnglibconf.h.prebuilt in INSTALL.
[libpng17] Port recent changes from libpng16 branch:

  Silence 'unused parameter' build warnings (Cosmin).
  $(CP) is now used alongside $(RM_F).  Also, use 'copy' instead
    of 'cp' where applicable, and applied other minor makefile changes.
  Don't warn about invalid dimensions exceeding user limits.
[libpng17] Allow an easy replacement of the default pre-built configuration

header with a custom header, via the make PNGLIBCONF_H_PREBUILT macro.
[libpng17] Complete the update of scripts/makefile.ne12bsd.
[libpng17] Fixed syntax of Copy command in makefile.amiga