Relax limits of FCurve Bézier handles during evaluation. FCurve handles
can be scaled down to avoid the curve looping backward in time. This
scaling was done correctly but over-carefully, posing unnecessary
limitations on the possible slope of FCurves. This commit changes the
scaling approach such that the FCurve can become near-vertical.
Bump Blender's subversion from 291.0.1 to 291.0.2 to ensure that older
animation files are correctly updated.
Reviewed By: sybren
Differential Revision: https://developer.blender.org/D8752
