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!

source/blender/src/space.c

@@ -3438,6 +3438,11 @@ static void winqreadseqspace(ScrArea *sa, void *spacedata, BWinEvent *evt)
 			if((G.qual==0))
 				transform_seq('g', 0);
 			break;
+		case KKEY:
+			if((G.qual==0)) { /* Cut at current frame */
+				if(okee("Cut strips")) seq_cut(CFRA);
+			}
+			break;
 		case MKEY:
 			if(G.qual==LR_ALTKEY)
 				un_meta();