Update libpng to 1.2.38 to patch a minor security issue.
diff --git a/scripts/descrip.mms b/scripts/descrip.mms
index 3584b0d..f3a8d7b 100644
--- a/scripts/descrip.mms
+++ b/scripts/descrip.mms
@@ -1,6 +1,6 @@
 
 cc_defs = /inc=$(ZLIBSRC)
-c_deb = 
+c_deb =
 
 .ifdef __DECC__
 pref = /prefix=all
@@ -29,7 +29,7 @@
    run pngtest
 
 clean :
-	delete *.obj;*,*.exe;*
+	delete *.obj;*,*.exe;
 
 
 # Other dependencies.
@@ -44,9 +44,9 @@
 pngmem.obj : png.h, pngconf.h
 pngrio.obj : png.h, pngconf.h
 pngwio.obj : png.h, pngconf.h
-pngtest.obj : png.h, pngconf.h
 pngtrans.obj : png.h, pngconf.h
 pngwrite.obj : png.h, pngconf.h
 pngwtran.obj : png.h, pngconf.h
 pngwutil.obj : png.h, pngconf.h
 
+pngtest.obj : png.h, pngconf.h