EditMode armature: mirrored editing feature.

- Option is in EditButtons, Armature panel.
- Currently only local X-axis mirror (seems to be default anyway)
- Transform then applies changes to the mirrored-name bone as well.
- Extrude: also does the counterpart Bone
- New: SHIFT+E extrude: extrudes 2 mirrored Bones out of a normal Bone.
  (creating names by appening _L and _R)

Or in short: you can now model a full rig without any manual naming!
Of course the names are not too nice... a couple of ideas to explore;
- rename a mirrored bone renames counterpart too
- allow in weightpaint mode to select Bones
- and of course mirrored edit in PoseMode (if that's useful...)

Important note: I tweaked the naming convention a bit; names like
Bone_L.005 and Bone_R.005 are considered counterparts. However, if
you use the "Flip names" option, the number extension is still
truncated.

BTW: Commits in Zr's code are fixes for gcc warnings. :)

source/blender/src/space.c

@@ -1184,7 +1184,7 @@ static void winqreadview3dspace(ScrArea *sa, void *spacedata, BWinEvent *evt)
 						else if(G.obedit->type==OB_SURF)
 							extrude_nurb();
 						else if(G.obedit->type==OB_ARMATURE)
-							extrude_armature();
+							extrude_armature(0);
 					}
 				}
 				else if (G.qual==LR_CTRLKEY) {
@@ -1196,6 +1196,9 @@ static void winqreadview3dspace(ScrArea *sa, void *spacedata, BWinEvent *evt)
 						initTransform(TFM_CREASE, CTX_EDGE);
 						Transform();
 					}
+					else if (G.obedit && G.obedit->type==OB_ARMATURE) {
+						extrude_armature(1);
+					}
 				}
 				break;
 			case FKEY: