1.0.9.11: even faster SLOT-VALUE &co

1.0.9.11: even faster SLOT-VALUE &co

* Move the SLOT-TABLE data to layout, so that it can be accessed
  faster, giving ~40% more speed to SLOT-VALUE &co using variable slot
  names. Speedup is due to one less level of indirection, and avoiding
  a GF call when fetching the table.

* FIND-SLOT-DEFINITION goes back to using the linear search, as in
  some cases where we use it the class wrapper may already be invalid.
  This will be re-addressed later.