[devel] Added an explicit make step to projects/vstudio for pnglibconf.h

Also corrected zlib.vcxproj into which Visual Studio had introduced
what it calls an "authoring error".  The change to make pnglibconf.h
simply copies the file; in the future it may actually generate the
file from scripts/pnglibconf.dfa as the other build systems do.
6 files changed