add "cache" flag to system_image

Author: jcupitt

share/nip4/start/_magick.def

@@ -77,9 +77,9 @@ Magick = class {
 	version
 		= map parse_int (split (member ".-") version_string)
 	{
-		output = vips_call9 "system"
-			["'" ++ command_path ++ "' -version"] [$log=>true,
-$revalidate=>true];
+		output = vips_call9 "system" ["'" ++ command_path ++ "' -version"] [
+			$log=>true
+		];
 		version_string
 			= (split (equal ' ') output)?1, use_gm
 			= (split (equal ' ') output)?2;

share/nip4/start/_stdenv.def

@@ -2399,8 +2399,14 @@ system_image command x
 	system im
 		= image_out
 	{
-		[image_out, log] =
-			im_system_image (get_image im) "%s.tif" "%s.tif" command;
+		[image_out, log] = vips_call9 "system" [command] [
+			$in => [get_image im],
+			$out => true,
+			$in_format => "%s.tif",
+			$out_format => "%s.tif",
+			$cache => true,
+			$log => true
+		];
 	}
 }