Extended mode enum for selecting affected axes for volume preservation.

Generalizing constraint volume preservation.

Moved settings for volume adjustment, limits and smoothing out of the
StretchTo constraint, so they can be reused by other constraints.

Allow disabling the volume exponent internally.

Added a "specials" menu button next to the particle systems list for
accessing the copy operator.

Changed the workflow for the particle system copy operator to the common
active-to-selected pattern.

New operator for copying (hair) particle systems from one object to
another, including edit data (grooming).

This uses basically the same method as the existing connect/disconnect
feature. The main difference is that it allows working with multiple
objects and transferring the //particle/hair data// instead of the
//mesh// data (which is what connect/disconnect expects). This is a much
more realistic workflow when rigging, topology etc. changes and
groomed hair has to be transferred to the changed model.

Removed unused particles pointer from particle edit data.

Fix T43254: Camera required for rendering sequencer scene

warning: unused var

Merge branch 'master' into gooseberry

New texture influence option for particle kink amplitude (as opposed to
frequency).

Renaming "Kink" texture influence to "Kink Frequency" to be more
specific.

Spiral rotation axis was not always fully normalized, avoid an assert.

Make random child length work again with the spiral kink mode.

Add missing stub to the player, so buildbot keeps delivering gooseberry builds

Merge branch 'master' into gooseberry

Allow clumping and roughness in Spiral kink mode as well.

This requires interpolating the parent key properties, because no single
parent key can be mapped to each key on the children any more.

Optional randomization factors for the spiral radius and axis orientation.

Support in Cycles for the extra spiral keys in hair paths.

Nicer calculation of the kink axis and result of the spiraling for
negative radius.