Add cil/varinfos request to server mode

[sim642]

This returns a list of data for all varinfos known to CIL, including:

1. vid to be used for other requests since name is not globally unique,
2. original_name to be used for mapping to actual code names (or detecting temporaries if missing),
3. role and function for determining the scope.

This is provided as a list and a client may construct suitably grouped mappings from it.

[sim642]

I added a richvarinfos request directly on master: db5843f. That should return all of those alloc variables.