Simplify using the Makefile for non-CL-hackers.

Try harder not to mix Common Lisp Developers profiles with main pgloader
expected audience who will not have a Quicklisp system ready, by doing
our magic Quicklisp calls in a pgloader specific directory.

That might impact #45 badly as the homebrew formula should need to now
install its Quicklisp distributions elsewhere, but it should be easy
enough to fix.

Also, systematically `git pull` from the local-projects dependencies we
need to work with to avoid some bad surprises to our users.