A batch of globaldb changes.

* Eliminate verbiage from and improve hygiene of DEFINE-INFO-TYPE.
  The :DEFAULT option, if a function, is called to produce
  a default. If not a function, it is treated as literal data.

* All values placed into globaldb are type-checked.
  Reading a value incurs no type-check.

* A list of proclaimed declarations for SB-CLTL2 is maintained
  without reference to info environments.

* :xc-constant-value is no longer handled through globaldb.