Blender Git Loki

Proof of concept pie interaction:

Press for calling operator, hold to spawn pie menu.

Test on object mode operator, pressing TAB toggles to edit mode, keeping
TAB pressed more that the drag timeout spawns a pie menu.

Still needs a way to enforce the menu to not listen for further drag
timeouts but looks like the concept holds.

This is implemented using the previous operator,
WM_OT_call_pie_menu_timer, in a macro. When the calling button is
pressed too long, the operator is cancelled (thus cancelling the macro)
but spawning a pie menu before that. If the timeout is not reached and
a key release event is detected, the operator finishes and the macro
continues, calling the next operator instead (object mode set, in our
case).