1.0.18.16: many STYLE-WARNING changes.

1.0.18.16: many STYLE-WARNING changes.

* Add various subclasses of STYLE-WARNING in src/code/condition.lisp
  for most of the cases signaled around the system.  (A few style
  warnings remain SIMPLE-STYLE-WARNINGS for now.)

* Make STYLE-WARN be like WARN (take a condition class name and
  arguments).

* Change over many callers of STYLE-WARN to supply names of new
  STYLE-WARNING classes and initargs for those conditions.

* Set the default value of SB-EXT:*MUFFLED-WARNINGS* to a type that
  includes uninteresting redefinitions of functions and methods.