wrong documented contract for check forms

[pnkfelix]

The check forms documented in SchemeUnit? API all say that checks produce #t.
See for example:

   (check op v1 v2 [message]) → #t

However, it actually produces the result of applying the op (if the op produced a non-false result. For example:

> (check + 2 3)
5

Thus the → #t part of the documentation is misleading.

[schematics]

Fixed in svn. Thanks.