Patch from Dan Weinreb:
limit the maximum number of request handler threads that a taskmaster may
create.
Support a new SOFT argument to the STOP function that makes Hunchentoot
wait until all currently outstanding requests have been processed before
returning.
Add a favicon.ico to the standard file tree.
Refactorings in the START-OUTPUT function to separate out the actual
header sending from the request processing part. The new SEND-RESPONSE
function does the I/O part of sending the response header (and possibly
content) and also does the logging. Used by the thread count limiting
code to send a 503 message if no more threads can be created.