I was getting a load-foreign-library-error on the following:
(define-foreign-library libcurl (:unix (:or "libcurl.so.3" "libcurl.so")) ((:not :unix) (:default "libcurl")))
(use-foreign-library libcurl)
until I patched try-foreign-library-alternatives as in the attached darcs patch, also at http://csserver.evansville.edu/~sc87/cffi/tfla-success.patch
If load-foreign-library is supposed to answer non-nil on success, a different patch is in order.