Remove a no longer necessary `impossible`
Make tests work with sandboxes
Fix GC statistics overflow
Reduce redundant 'specifically' clauses in errors
Update expected error messages for tests
Improvement for 'auto'

Now proof search can be deferred if there are too many metavariables in
the goal - previously in this case it would happily pick any old
solution causing weird errors elsewhere in some cases.
Need to resolve autos in each 'try' branch

If the branch solves an implicit which makes the auto solvable, we need
to try to resolve it straight away so we know whether the branch is
valid or not. We need this especially when using 'try' to implement
implicit coercions.
Define Show instance for Vect via toList.
Merge pull request #1712 from Melvar/remove-impossible

Remove a no longer necessary `impossible`
Merge pull request #1755 from mattias-lundell/master

Make tests work with sandboxes and fix GC statistics overflow
Merge pull request #1761 from bmsherman/dontDupErrors

Reduce redundant 'specifically' clauses in errors
Merge pull request #1763 from ziman/show-vect

Define `Show` instance for `Vect` via `toList`
Check target of 'with' is a value (not a function)
Avoid retrying unification problems constantly

If solved metavariables do nothing to a unification problem, there's no
point in trying it again - this can lead to a massive slowdown if
there's a lot of evaluation in the type. Partially addresses #1219.

Fixes #1716 on the way by tidying up type of updateProblems.
Add a default case for addShows

The assumption that the argument lists are equal in length is a flawed
one. Fixes #1765
sharingan