1.0.35.15: Add and export various functions related to type specifiers.

1.0.35.15: Add and export various functions related to type specifiers.

  * TYPEXPAND-1, TYPEXPAND, TYPEXPAND-ALL work like their MACROEXPAND
    counterparts except that they expand type specifiers.

  * DEFINED-TYPE-NAME-P returns whether a symbol is known to name a
    type specifier.

  * VALID-TYPE-SPECIFIER-P returns whether a (possibly compound) type
    specifier is known, and syntactically / structurally correct. A
    type specifier is valid if it is to be accepted as second argument
    by TYPEP -- except that VALID-TYPE-SPECIFIER-P can also deal with
    FUNCTION and VALUES type specifiers.

  * Export these functions from SB-EXT.