Change case of blend mode names to match PD convention
Force the blend mode dropdown to display the full list of modes

In an ideal world, we'd simply display separators between the various
layer mode groups.  But that requires a fully owner-drawn combo box,
which is a huge project, and not something I want to spend time on right
now.

In the meantime, this will at least allow users to see the full list of
blend modes without manual scrolling.

(FYI: I don't think this technique works on XP.)
Fix memory leak in Image -> Rotate Arbitrary