Blender Git Loki

Patch provided by Matt Ebb, cut sequence strips (patch tracker).
There were a couple of issues with the implementation:

- there was no proper test if selected strips would be cut or not
- cutting meta strips could go very wrong... for example when the cut
of meta was in an internal gap. With meta's being recursive, and too
complex, I've disabled Meta-cutting
- added an OK menu for hotkey K
- added warnings when no cut was done

This is the first time in 6 years I do work in sequencer... man, this has
grown into a messy bizz! Like sequence variables... using names like:
start, startdisp, startstill, startoffs... totally confusing here. Could
use giant cleanup! Implementation was weak from scratch though, Mea Culpa!