[Bf-codereview] Fix for BMesh Bevel Operator (issue 5967069)

[TrumanBlending at gmail.com]

Reviewers: bf-codereview_blender.org,

Description:
This patch fixes issues with the current bevel operator.
1. Correct absolute distance bevelling. The user can now specify an
absolute distance which all edges will then be offset. This doesn't work
in the trunk bevel op.
2. Better defaults. Now by default it is set up to do absolute distance
bevel.
3. Consistency. Options are now named in the same fashion as the inset
operator for consistency between tools. The options also have the same
effects as other tools.

Please review this at http://codereview.appspot.com/5967069/

Affected files:
   source/blender/bmesh/intern/bmesh_opdefines.c
   source/blender/bmesh/operators/bmo_bevel.c
   source/blender/editors/mesh/editmesh_tools.c