Making DO-FINALLY more useful

Now DO-FINALLY finishes the returned promise with the values of the
given promise (instead of the return values of the given function).
Fix wrap-callback

Ensures that *promise-keep-specials* works for all links of the promise chain.
Merge pull request #10 from archimag/imporving-do-finally

Making DO-FINALLY more useful
Merge pull request #11 from archimag/fix-wrap-callback

Fix wrap-callback