* srfi-13.c (scm_string_any, scm_string_every): Add support for char
        and charset as predicates, per SRFI-13 spec.

I slipped this into 1.6 too, since it's a deviation from the spec.
New words:


 -- Scheme Procedure: string-any char_pred s [start end]
     Return true if `char_pred' is satisfied for any character in the
     string S.  CHAR_PRED can be

        * A character, to to test for any in S equal to that.

        * A character set (*note SRFI-14::), to test for any character
          in S in that character set.

        * A predicate function, called as `(CHAR_PRED c)' for each
          character in S, from left to right, to test for any on which
          CHAR_PRED returns true.

          When CHAR_PRED does return true (ie. non-`#f'), that value is
          the value returned by `string-any'.

     If there are no characters in S (ie. START equals END) then the
     return is `#f'.

     SRFI-13 specifies that when CHAR_PRED is a predicate function, the
     call on the last character of S (assuming that point is reached)
     is a tail call, but currently in Guile this is not the case.

 -- Scheme Procedure: string-every char_pred s [start end]
     Return true if CHAR_PRED is satisifed for every character in the
     string S.  CHAR_PRED can be

        * A character, to to test for every character in S equal to
          that.

        * A character set (*note SRFI-14::), to test for every
          character in S being in that character set.

        * A predicate function, called as `(CHAR_PRED c)' for each
          character in S, from left to right, to test that it returns
          true for every character in S.

          When CHAR_PRED does return true (ie. non-`#f') for every
          character, the return from the last call is the value
          returned by `string-any'.

     If there are no characters in S (ie. START equals END) then the
     return is `#t'.

     SRFI-13 specifies that when CHAR_PRED is a predicate function, the
     call on the last character of S (assuming that point is reached)
     is a tail call, but currently in Guile this is not the case.