Lint initial(thing.var), where var is a list

[spookydonut]

Closes #284

[SpaceManiac]

1. Error message should be more descriptive about what the issue is. Along the lines of:
   initial() called on var/list/{}, but it always returns null for lists
2. The for loop here will give redundant errors if you write initial(a.b.c.d). Should probably just pull .last().
3. It might make sense to apply this to anything that isn't a primitve, rather than lists, because new /obj likewise returns null from initial().
4. Could go either way on this but it might make sense to analyze the actual initial values of that variable for subtypes to see if they are non-primitives, rather than just the static types.