Blender Git Loki

Bugfix #4351

ESC wasn't supported for sequence-based rendering yet.
Solved it with correctly initializing the sequence render with all
render callbacks, including render updates (which it didn't do yet).

Cleanup:

- Bug in ghostwinlay code: the get_mbut() function reads from the window
struct if a mouse is pressed. However, when you press the mouse in the
sequencer, which causes a render, this value was hanging because then
the active window was a render window.

- The new render display options (image window) didn't work for sequence
render OK. There was a recursion even, because a sequence draw command
calls a render, which in turn now calls redraws.