[plt-scheme] changes to contract library in CVS

I've just finished some changes to the contract library in CVS.
Essentially, this is just a name cleanup (and some of these names
changed a while back). Here's the overall renames from v208:

      not/f => not/c
      box/p => box/c
      cons/p => cons/c
      vector/p => vector/c
      list/p => list/c
      any? => any/c
      printable? => printable/c
      false? => false/c
      natural-number? => natural-number/c

In addition, I've just added exact-integer-in, as suggested by Doug
Williams (I decided to stick with the longer name because our
documentation already has many uses of "exact integer in" as an English
phrase. Perhaps we should change it everywhere at some point, tho.)

Robby