adjust check syntax to track which submodule a reference occurs in

so that arrows point to the relevant requires only, not to all requires

this commit also changes the handling of module+ (aka module* w/ #f) so
that it doesn't count as an "inner" module anymore
use the name in the exists contract in its error message
fix default node pict so it doesn't draw outside of its bounding box

and make the size a little bit bigger
Allow inference when the result has free variables.
Remove special case of subtype in tc-apply.
Add missing %s and corresponding unit tests.
Correctly extend tvars in the right place during inference.

Removes wrong extension of tvars in apply as well.
Make polydotted case more standard.
Handle inference of list dots under regular lists.
Make inference work with lists under dotted lists.
Infer in dotted lists when we can infer on the bound.
Support keywords with %.
Make infer-tests give better errors.
Correct subst/dots on list-dots and values-dots.
Add some more results to infer-tests.
fix minor stepper damage caused by a9f46ade9ea16eba7507
simplify stepper and fix unevaluated id bug
tiny test for letrec
make plot tests more drdr friendly

This avoids a race-condition when one test deletes the file
that another creates and also avoids cluttering the current
directory.
Unbreak TR contracted build.