support for .INSTALL file

abuild

@@ -173,6 +173,10 @@ package_apk() {
 	echo "$depends" > "$db/DEPEND"
 	echo "$url" > "$db/WWW"
 	local i
+	if [ -n "$install" ]; then
+		cp "$srcdir/$install" "$dir/.INSTALL" || return 1
+		chmod +x "$dir/.INSTALL"
+	fi
 	for i in pre-install post-install pre-deinstall post-deinstall; do
 		[ -f ../$i ] && cp ../$i "$db"/
 	done