misc minor changes
- make it clear that navmesh visualize option only works in path mode.
- use 2 decimal places for motion-blur shutter speed (user request).
- use 'const' for some bmesh functions.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55584 954f8c5b-7b00-dc11-b283-0030488c597c
improve beauty-fill tool for non-flat triangles.
Project the triangle pair into 2d coords before measuring.

before/after - http://www.graphicall.org/ftp/ideasman42/beauty_fill_fix.png

note: I committed this r54403 but it caused eternal looping so I reverted for 2.66 release.
ran extensive tests and its not giving problems so re-applying this improvement.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55585 954f8c5b-7b00-dc11-b283-0030488c597c