[devel] Revised scripts/makefile.netbsd, makefile.openbsd, and makefile.sco

to put png.h and pngconf.h in $prefix/include, like the other scripts,
instead of in $prefix/include/libpng.  Also revised makefile.sco
to put them in $prefix/include/libpng12 instead of in
$prefix/include/libpng/libpng12.
7 files changed