[libpng16] Added pngconfig.h file.  This indirect reference to config.h avoids

problems with build scripts that search for config.h and find an
inappropriate one in the standard paths.
diff --git a/scripts/makefile.ne12bsd b/scripts/makefile.ne12bsd
index 3bfd3f8..ac30ab8 100644
--- a/scripts/makefile.ne12bsd
+++ b/scripts/makefile.ne12bsd
@@ -21,7 +21,7 @@
 SRCS=	png.c pngset.c pngget.c pngrutil.c pngtrans.c pngwutil.c \
 	pngread.c pngrio.c pngwio.c pngwrite.c pngrtran.c \
 	pngwtran.c pngmem.c pngerror.c pngpread.c
-INCS=	png.h pngconf.h pnglibconf.h
+INCS=	png.h pngconf.h pnglibconf.h pngconfig.h
 MAN=	libpng.3 libpngpf.3 png.5
 
 CPPFLAGS+=-I${.CURDIR}