The option currently only works within the same build environment where
the image was first build, as noted in #133. This is an attempt at
convincing ASDF not to load systems that pgloader depends on in order to
be able to load only the new pgloader definition.
While it looks sound in principle, I failed to have it work in the lab.
Given that previous to this patch nothing works at all, it's not a
regression, let's push it as is makes the code saner.
Also, it looks like asdf::*immutable-systems* is what we want here, but
that's asdf 3.1.x and we're not there yet.
Loading external libs at application startup time is not convenient as
it forces users to install freetds everywhere even when they don't need
it. This patch makes it so that freetds is only loaded when pgloader is
asked to load from a MS SQL database source.
Note that we could have done the same for SSL if it wasn't possibly used
to connect to PostgreSQL, which isn't optional in current pgloader
implementation.
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.
