#1 Optional inputs and context problems

[Bruno Nicoletti]

V1.0 leaves an ambiguity on how a plugin should manage optional
input clips. A plugin has no way of knowing if a host supports
optional inputs in a specific context.

Currently it is assumed that a host can support optional input clips
in all contexts, this many not be true, and can cause problems.

For example, a plugin, which is designed to work with an optional
input in the filter context may have parameters to control how to
use that input, and be designed with a certain work flow. When
running on a host that does not allow optional inputs, this will
cause all sorts of confusion and frustrations on a users behalf.

If a plugin can detect that a specific host does not support optional
inputs, it can modify it's behaviour accordingly.