Blender Animation: Jog keys

This patch implements a simple version of 'jog keys'.

Functionality:
Alternative keys for animation playback:
ALT + Right Arrow: Start animation playback forward or increase speed if already playing
ALT + Left Arrow: Start animation playback backward or increase speed if already playing backwards

The speed is currently clamped at 6x normal speed.

Implementation Notes:
This is a cleaned up version of a previous commit that had issues - if I remember correctly the playback buttons weren't working as expected anymore. I have tested the current patch and it seems ok.
The jog keys are disabled if the animation is synched to the sound (AV-sync) and playing forward - in my view it also doesn't make sense to speed up if you synch to the sound.

Waiting for feedback :)

[brechtvl, 2011-03-17 10:43:26]

Thanks for using the system, nice to see it getting used, some comments below.

http://codereview.appspot.com/4298043/diff/1/source/blender/editors/screen/sc...
File source/blender/editors/screen/screen_ops.c (right):

http://codereview.appspot.com/4298043/diff/1/source/blender/editors/screen/sc...
source/blender/editors/screen/screen_ops.c:2758: if((scene->audio.flag &
AUDIO_SYNC) && !(sad->flag & ANIMPLAY_FLAG_REVERSE) && finite(time =
sound_sync_scene(scene)))
This doesn't seem consistent with ED_screen_animation_play, there playing sound
is disabled if speed != 1, probably should do that here too.

http://codereview.appspot.com/4298043/diff/1/source/blender/editors/screen/sc...
source/blender/editors/screen/screen_ops.c:2895: speed_mul = (sad->speed_mul <
ANIMPLAYER_MAX_SPEEDMUL) ? sad->speed_mul+1 : ANIMPLAYER_MAX_SPEEDMUL;
I was expecting each key press to double speed, and then have the max 16 or so.
That's mostly based on what I'm used to in video players though.

Actually why not make speed_mul a float, and make it possible to halve the
playback speed too using these keys?

http://codereview.appspot.com/4298043/diff/1/source/blender/editors/screen/sc...
source/blender/editors/screen/screen_ops.c:2944: RNA_def_boolean(ot->srna,
"toggle", 1, "Toggle", "Toggle forward/backward rather than stopping the
animation");
This description is not clear to me. Maybe flip the boolean and call it
adjust_speed?

[brechtvl, 2011-03-17 10:48:30]

Also, maybe add Joshua to the reviewers, assuming you discussed this with him
last time?

[elubie, 2011-03-19 21:05:52]

Thanks for the review Brecht, new version here.

[aligorith, 2011-03-20 10:11:46]

Just a quick comment: 
I think we should postpone this, at least until after 2.57 is released, since
the underlying code here is starting to get quite hairy. In particular the long
chains of args that need to be passed in. It's all getting a bit out of control,
so adding this on seems to just make matters worse.