2.5 - Assorted Animation UI/Editing Tweaks

Main Feature:
* It is now possible to choose which AnimData block is the 'active' one for editing, and/or select them too. AnimData blocks are generally the dark blue and lighter-blue expanders (i.e. Scene, Object, Camera, Lamp, Curve, Armature, etc.)

* Objects are no longer selected/deselected when AKEY is used to toggle selection of channels. This was getting a bit annoying. 

* Following on from selection of AnimData blocks, it is now possible to select/make active an AnimData block in the animation editors, and change the active action for that block via the 'Animation Data' panel in NLA Editor's properties region.
--> Be aware that user-counts are not totally handled correctly there yet, so some funky behaviour might be seen...
--> It is possible to assign a new action, or to assign an existing one, allowing to switch between actions as in the past with Actions/IPO Editors...

Other tweaks:
* Some code tweaks towards making the 'Euler Filter' feature for Graph Editor working sometime soon
* Added some backend code for snapping the values of keyframes to a single value. Still need to work out some UI for it though.
* Shuffled the code for ACT_OT_new() around, and removed the poll() callback so that it worked in NLA too.
* Fixed some more notifier bugs with deleting bones and a few other editmode operations for Armatures.

source/blender/editors/include/ED_keyframes_edit.h

@@ -73,6 +73,7 @@ typedef enum eEditKeyframes_Snap {
 	SNAP_KEYS_NEARSEC,
 	SNAP_KEYS_NEARMARKER,
 	SNAP_KEYS_HORIZONTAL,
+	SNAP_KEYS_VALUE,
 } eEditKeyframes_Snap;
 
 /* mirroring tools */