Automatically slide when moving loops

[jlampel]

Right now, tweaking verts and edges will always perform a freeform move. But, in many cases, we actually need a slide. Having a good heuristic for when to automatically slide instead of move should make things 'just work' without the user having to think about it. I will try a few things out, but here are my initial thoughts:

• Never slide if the selection includes faces.

• Only slide when all selected edges are paralell to the surrounding selected edges. If the selection includes edges that are not along the same loop (i.e. branch off in a different direction), sliding will pretty much always result in a mess. This test should also account for having multiple selected loops. Open question - what about edge selections that run through poles?

• Only slide when more than x number of verts are selected. By default it could be 3, and this could be a user configurable value next to the option to turn automatic sliding off.