Sticky Keys backend

Design task: T42339
Differential Revision: D840
Initial implementation proposal: T41867

Short description:
With this we can distinguish between holding and tabbing a key. Useful
is this if we want to assign to operators to a single shortcut. If two
operators are assigned to one shortcut, we call this a sticky key.

More info is accessible through the design task and the diff.

A few people that were involved with this:
* Sean Olson for stressing me with this burden ;) - It is his enthusiasm
that pushed me forward to get this done
* Campbell and Antony for the code and design review
* Ton for the design review
* All the other people that gave feedback on the patch and helped to
make this possible

A big "Thank You" for you all!

1 files changed, 8 insertions, 5 deletions

diff --git a/source/blender/editors/space_node/node_relationships.c b/source/blender/editors/space_node/node_relationships.c
index c8951a1172e..f72def8377f 100644
--- a/source/blender/editors/space_node/node_relationships.c
+++ b/source/blender/editors/space_node/node_relationships.c
@@ -633,11 +633,14 @@ static int node_link_modal(bContext *C, wmOperator *op, const wmEvent *event)
 		case RIGHTMOUSE:
 		case MIDDLEMOUSE:
 		{
-			node_link_exit(C, op, true);
-			
-			ED_area_headerprint(CTX_wm_area(C), NULL);
-			ED_region_tag_redraw(ar);
-			return OPERATOR_FINISHED;
+			if (event->val != KM_NOTHING) {
+				node_link_exit(C, op, true);
+				
+				ED_area_headerprint(CTX_wm_area(C), NULL);
+				ED_region_tag_redraw(ar);
+				return OPERATOR_FINISHED;
+			}
+			break;
 		}
 	}