changed bpy.ops.pose.select_flip_active() to
bpy.ops.pose.select_mirror() for compatability with 2.70
oops. Now this really works with blender 2.70:
- Changed select_mirror and keyframe_insert logic to work on 2.70
- Added support for flipping animations where not all bones are in
  visible layers
Fix script for Blender 2.70. Now it's not required to enable "Automatic keyframe insertion" button.
Merge pull request #2 from morevnaproject/master

Fix script for Blender 2.70. Now it's not required to enable "Automatic keyframe insertion" button for script to work.