Second itteration of global undo system. Now based on:

- file-to-memory save
- incremental difference steps (compression)

everthing has been tightly coded to use minimum of memcpy or allocs. In
fact this system works with a single full buffer (=file) in memory, and undosteps as differences from it.
Speed gain is factor 4-8 faster. I've added it in CTRL+ALT+T timer menu for
a test. Please note the gain is especially in the undo-storing, not in
retrieving undo.

Also new: file read option to skip UI read (file menu). This now also is
default for the undo system.

source/blender/src/oops.c

@@ -105,6 +105,7 @@ Oops *find_oops(ID *id)
 	return oops;
 }
 
+/* never even called! (ton) */
 int test_oops(Oops *oops)
 {
 	/* test if own ID block still exists */