Integration of new IK lib features in Armature Poses.

Best is to forget yesterday's commit and old docs. New docs are underway...

Here's how IK works now;

- IK chains can go all the way to the furthest parent Bone. Disregarding
  the old option "IK to Parent" and disgregarding whether a Bone has an
  offset to its parent (offsets now work for IK, so you can also make
  T-bones).
- The old "IK to Parent" option now only does what it should do: it denotes
  whether a Bone is directly connected to a Parent Bone, or not.
  In the UI and in code this option is now called "Connected".
- You can also define yourself which Bone will become the "Root" for an IK
  chain. This can be any Parent of the IK tip (where the IK constraint is).
  By default it goes all the way, unless you set a value for the new IK
  Constraint Panel option "Chain Lenght".
- "Tree IK" now is detected automatic, when multiple IK Roots are on the
  same Bone, and when there's a branched structure.
  Multiple IK's on a single chain (no branches) is still executed as usual,
  doing the IK's sequentially.
- Note: Branched structures, with _partial_ overlapping IK chains, that don't
  share the same Root will possibly disconnect branches.
- When you select a Bone with IK, it now draws a yellow dashed line to its
  Root.
- The IK options "Location Weight" and "Rotation Weight" are relative,
  in case there's a Tree IK structure. These weights cannot be set to
  zero. To animate or disable IK Targets, use the "Influence" slider.
- This new IK is backwards and upwards compatible for Blender files.
  Of course, the new features won't show in older Blender binaries! :)

Other changes & notes;

- In PoseMode, the Constraint Panel now also draws in Editing Buttons, next
  to the Bones Panel.
- IK Constraint Panel was redesigned... it's still a bit squished
- Buttons "No X DoF" is now called "Lock X". This to follow convention to
  name options positive.
- Added Undo push for Make/Clear Parent in Editmode Armature
- Use CTRL+P "Make Parent" on a single selected Bone to make it become
  connected (ALT+P had already "Disconnect").

On todo next; Visualizing & review of Bone DoF limits and stiffness

source/blender/src/transform_conversions.c

@@ -382,8 +382,8 @@ void count_bone_select(TransInfo *t, ListBase *lb, int do_it)
 		do_next= do_it;
 		if(do_it) {
 			if (bone->flag & BONE_SELECTED) {
-				/* We don't let IK children get "grabbed" */
-				if ( (t->mode!=TFM_TRANSLATION) || (bone->flag & BONE_IK_TOPARENT)==0 ) {
+				/* We don't let connected children get "grabbed" */
+				if ( (t->mode!=TFM_TRANSLATION) || (bone->flag & BONE_CONNECTED)==0 ) {
 					bone->flag |= BONE_TRANSFORM;
 					t->total++;
 					do_next= 0;	// no transform on children if one parent bone is selected
@@ -402,8 +402,8 @@ static int add_pose_transdata(TransInfo *t, bPoseChannel *pchan, Object *ob, Tra
 
 	if(bone) {
 		if (bone->flag & BONE_TRANSFORM) {
-			/* We don't let IK children get "grabbed" */
-			if ( (t->mode!=TFM_TRANSLATION) || (bone->flag & BONE_IK_TOPARENT)==0 ) {
+			/* We don't let connected children get "grabbed" */
+			if ( (t->mode!=TFM_TRANSLATION) || (bone->flag & BONE_CONNECTED)==0 ) {
 				
 				VECCOPY(vec, pchan->pose_mat[3]);
 				VECCOPY(td->center, vec);