Make the scene preview range not clamp the start/end values

This will make this consistent with the behaviour of other start/end
ranges in blender. So start/end will instead be adjusted to always
satisfy the "start >= end" requirement instead of clamping the values.

Fix cloth triangle area calculation being wrong

Before the area calculated was for the resulting quad, not the triangle.
So just simply divide the result by 2.

Add the ability to create internal springs to the cloth sim

This can be used to make closed surfaces behave more like a soft body.

Reviewed By: Jacques Lucke

Differential Revision: http://developer.blender.org/D5788

Fix crash when trying to decimate baked fcurve channels

No curve data was available for the modal decimate operator.
Added a check for when the curve has baked data.

Make curve decimation only take into account the selected curve points

Previously the decimation would take the whole curve into account when
decimating and not just the selected part.

This also contains various smaller bug fixes for the fcurve decimation.

Reviewed By: Sybren

Differential Revision: http://developer.blender.org/D6286

Add cloth pressure vertex group and unlock cloth shrink values range

Introduced a way to specify cloth pressure force influence with a vertex
group. This will allow users to only have pressure affect certain parts
of the mesh.

In addition to this, the "shrink factor" is now also unlocked to allow
negative values and thus allowing the cloth mesh to grow as well.

Reviewed By: Jaques Lucke

Differential Revision: http://developer.blender.org/D6347

Fix T30941: Add cloth air pressure simulation

This adds some basic simulation of internal air pressure inside of
closed cloth mesh objects.

Reviewed By: Jacques Lucke

Differential Revision: http://developer.blender.org/D5473

Fix T62631: Cloth vertex mass capped to a very low number on scaled scenes.

Removed the weight limit and made the setting more clear in what it actually does.
IE, it controlls the weight of the vertices of the cloth mesh

Reviewed By: Brecht

Differential Revision: http://developer.blender.org/D5450

Add curve decimate in the graph editor

Added a animation curve decimate operator in the graph editor

Reviewed By: Sybren

Differential Revision: http://developer.blender.org/D4841

Fix python error when trying to delete presets

In some cases the default data paths for blender does not exist.
For example on windows when using the portable install.

This would lead to errors when trying to lookup default paths in
is_path_builtin. Now we handle cases like this gracefully.