Example: "-cc,+di | +di | "

Note the introduction of the 'or' operator.

This example would use the '-cc,+di' look, if it exists without error.
If this look does not resolve (due to a missing file), then the "+di"
look will be used. If that doesn/t succeed, then a 'no look' will be
used. (Note the trailing |). If one didn/t want the 'no look' option to
be used as a fallback, the last | operator would be omitted.

We also expose a function, so given a processor, one ca
query which look(s) were actually used.

-- Jeremy