Saving the new ControlList interpolation methods (enum) breaks loading
the session in older version. The session-format version will
need to be increased.
Until then:
* Fader automation + region gain envelope uses linear fades
* The automation-line visible in the GUI does not match the actual fade
(the y-axis is log/exp-scale, the fade is linear)
* Adding new points on the line is not using the correct initial value
* Custom changes of interpolation mode are not available
Neither of these issues is a regression.
8cd8cb1650