Patch offsets fix

It turns out that V_NOSCALESTART is dumb and breaks patch left/top offset scaling unless V_OFFSET is also set ...but V_OFFSET itself doesn't support V_FLIP, bleh.

So, what I have done in the following branch is:

• Fix V_OFFSET for now so that it supports V_FLIP.
• Make sure V_OFFSET does nothing without V_NOSCALESTART, as otherwise it might do strange things to your patch's position I expect.

I eventually plan to kill V_OFFSET and put in its place a more useful flag for 2.2, most likely a vertical version of V_FLIP (wouldn't that be great). This merge request is the first step in making that happen, you could say.