saugns v0.3.5c. Fix crash on updating ignored operator, timing.

Fixes:
 * Make parseconv ignore updates for operator nodes
   which weren't processed before, because the list
   in which they were created was cleared in the same
   event. Fixes crash in versions v0.3.5 and v0.3.5b.
   (Add 'devtests/ref-unused_node.sau' for testing.)
 * Add missing default time handling for
   an operator's second amp. and freq. ramps.
   (Rebased down to v0.2.13.)
 * Fix a case where the first part of a composite event
   is given infinite time by default, messing up script
   timing (negative never-ending duration, event order).
   (Rebased down to v0.2.3.)

(The crash also happened with v0.3.4, but not
v0.3.3 and v0.3.4b. Versions earlier than v0.3.3
ran, but changed data for the wrong operator.)
This tag has no release notes.