Fix comments: STRING-INPUT-STREAM-STRING is read-only and simple.
Freeze INTERPRETED-FUNCTION type
Add expected results for #\` expansion incl. pvk's change f2503917.

All will pass with the new implementation, pending commit.
Fix indentation
Fix &OPTIONAL + &REST handling in FIND-OPTIONAL-DISPATCH-TYPES

Previously, certain combinations of proclamations and definitions, such as

  (declaim (ftype (function (symbol &optional t &rest t)) foo))
  (defun foo (x &optional y &rest z))

lead to bogus STYLE-WARNINGs about mismatches between proclamation and
definition:

  The definition has one optional arg, but proclamation has zero.

This was caused by the simplifications of function types

     (function (symbol &optional t &rest t) symbol)
  ~> (function (symbol &rest t) symbol)

which FIND-OPTIONAL-DISPATCH-TYPES did not take into account.
Fix ftype proclamation and definition of ASSERT[-SYMBOL-HOME]-PACKAGE-UNLOCKED

* The ftype proclamation for ASSERT-SYMBOL-HOME-PACKAGE-UNLOCKED could
  be tightened.

* The lambda-list of the ASSERT-SYMBOL-HOME-PACKAGE-UNLOCKED stub in
  src/code/cross-misc.lisp differed from the ftype proclamation and the
  actual implementation. Fixing it exposed the bug fixed in c6f864d.