small magick improvements

Author: jcupitt

TODO

@@ -1,13 +1,4 @@
-- is the magick menu caching correctly? we see a lot of forking for each
-  action
-
-	eg. Annotate runs the annotation 9 times as the row evaluates
-
-	system should cache on the input file pointer plus the cmd string
-
-	removed NOCACHE from system, still runs 9 times :(
-
-- magick menu should use magick7
+- add magick7 support to _magick.def
 
 - get judder with rotate and images smaller than the window