Blender Git Loki

Error/Warning report flipping.

An operator Error throws up a menu, a Warning only a flashy header print.
In mesh editmode the menus for simple failures got very annoying, like
"Already a face" for Fkey on a face.

Proposal is to use warning for contextual failures, like:
- wrong selection
- unsupported combination
- wrong modes

And use errors for cases you really need user attention, for example when
issues are invisble or potentially damaging work.
- Memory failures
- Files not found

List can grow in future :) let's test this for mesh now.
I'll tackle this for other ops later after review.

(Also changed: loopcut disabled when editmode shows deformed result)