For the generated binary to be really portable, we need to be able to
open openssl 1.0.1 even when we've been built against openssl 1.0.0.
A way to achieve that with SBCL is by forcing the unloading of the lib
at image saving time and register a hook to load it again at image init
time. Using the proper API, CFFI will happily load the available file
for the lib rather than insisting on loading the exact same one than
found on the build machine.
