Tweaks to bevel and crease transform

They were using INPUT_SPRING in a way which didn't allow
it to easily redo the operator because INPUT_SPRING internally
is stored as a ration between old value and new one and crease
and bevel were converting this to value delta.

Now made it special input type INPUT_SPRING_DELTA which is
storing delta of the spring, meaning now values in the redo
panel kind of makes sense -- they mean how much to add/remove
to the crease/bevel weight.

Expect to be no functional changes from interactive transform
POV, just a bit more convenient to use redo panel.
Fix T40489: Curve drawing skipped loose-wire when mixed with solid faces
Fix for dupli's ignoring color in set-scenes

also skip setting wire color drawing depth
Freestyle: Fix for a potential infinite loop in stroke resampling by vertex count.

Changes were made in Stroke::Resample(int) in C++ to prevent a potential infinite loop
caused by an inconsistency between Stroke::_Length and the stroke length computed
based on stroke vertices.  Such a stroke length inconsistency is usually caused by missing
calls of Stroke::UpdateLength() (i.e., API implementation bugs), but also may occur due
to scripting errors in user-defined style modules.  This commit is meant to help script
writters to identify the latter error cases.  Now Stroke.resample(int) may raise a runtime
error to signal an error condition.
OSX 10.10: fix for Blender crashing on fsmenu due icloud in the favorite list but pointer is NULL when not activated
This does not break other OSX versions, just add a check for pathString
Optimize editmode drawing edgees

Was interpolating and setting the color twice per edge.
Now only set the color when needed (can be once per draw),
~2x speedup for edge drawing.
Fix T40456: cycles bug with branched path + sss + no sample all direct lights.
Fix issues when ungrouping meta changes the final sequencer render

Seems to be caused by the way how the most bottom strip in the stack
used to apply effect. Just rendering strip in this cases will not give
proper results.

Made it so effect is applying between empty imbuf and actual strip.
Seems to work by tests, but more intense testing is required.
Fix T40478: wrong cycles fresnel with GLSL materials in the viewport.
Fix T40482: Cycles matlib file crashes

it's possible that runtime optimizer would call get_attribute
with NULL renderstate. As per documentation, it's valid to
return false in that cases and in worst case we'll just miss
some possible optimization.

Supporting such cases would require some bigger changes to
Cycles since attributes are only set to up for the kernel
after shader compilation.

Thanks Brecht for review!
BMesh: avoid using OpenMP when nothing to do

Gave slowdown drawing on high poly meshes
Freestyle: Fix for a wrong formula used for RGB to grayscale conversion.

This bug fix is likely to affect the visual results of existing Freestyle setups using the
Material color/alpha/thickness modifiers with the 'material_attribute' parameter set to
either 'Diffuse' (default) or 'Specular', and also the Ramp option enabled in the case
of the Material color modifier.
Fix T40423: UV Editing 'Draw Other Objects' fails with Cycles
Freestyle: Fix for Interface0DIterator.object docstring with additional notes.
Correct hard-coded height for UV-Vertex buttons
Blender Internal: Fix for lamp option "Specular" not working when "Only Shadow" is enabled.

This is followup to rB8008d9bdfd57. Blender Render and GLSL preview
now produce the same results.
Fix T40436: No preview in Brush with Cycles

More like a feature request, but after i've implemented preview for
icons it was rather simple to support nodes previews.
Code cleanup: mixup hflag/htype
Avoid openmp sections in BM_mesh_elem_index_ensure
Fix T40382: 2D stabilization uses disabled markers

This lead to unpredictable results in some cases.