Install the Python DLL with execute priviledge set. This is required for

Cygwin Python to startup correctly when in ntsec mode.  Cygwin operating in
this mode is probably not the only system with this requirement.

Makefile.pre.in

@@ -535,7 +535,7 @@ altbininstall:	$(PYTHON)
 	else	true; \
 	fi
 	if test -f "$(DLLLIBRARY)"; then \
-		$(INSTALL_DATA) $(DLLLIBRARY) $(BINDIR); \
+		$(INSTALL_SHARED) $(DLLLIBRARY) $(BINDIR); \
 	else	true; \
 	fi