[libpng16] Fixed an incorrect separator ("/" should be "\") in

scripts/makefile.vcwin32 (bug report from Wolfgang S. Kechel).  Bug was
introduced in libpng-1.6.11.  Also fixed makefile.bc32, makefile.bor,
makefile.msc, makefile.intel, and makefile.tc3 similarly.
diff --git a/scripts/makefile.bor b/scripts/makefile.bor
index 254de89..c4eed60 100644
--- a/scripts/makefile.bor
+++ b/scripts/makefile.bor
@@ -59,8 +59,8 @@
 LDFLAGS=-M -L$(ZLIB_DIR) $(MODEL_ARG) $(LDEBUG)
 
 # Pre-built configuration
-# See scripts/pnglibconf.mak for more options
-PNGLIBCONF_H_PREBUILT = scripts/pnglibconf.h.prebuilt
+# See scripts\pnglibconf.mak for more options
+PNGLIBCONF_H_PREBUILT = scripts\pnglibconf.h.prebuilt
 
 ## Variables