1.0.29.52: small UCD optimizations and related cleanups

1.0.29.52: small UCD optimizations and related cleanups

* Fix "optimization failure with anything using
  SB-IMPL::UCD-GENERAL-CATEGORY" reported by Lynn Quam
  (https://bugs.launchpad.net/sbcl/+bug/392206) and related
  performance issues.

  ** Declare returns types of UCD accessors where it seems to matter.

  ** Make the character database a global variable, not special.

* Delete stale header comments from target-char.lisp: not just ASCII
  for quite a while now.

* Delete references to fonts and bits from docstrings everywhere but
  in CHAR-INT and canonicalize docstring indentation.

(The patch is a bit noisy because moving the definition of the
character database inside the macrolet messed up a whole bunch of
indentation -- sorry about that.)