Add :col-name DAO slot initarg

The sql name of a given DAO class' slot can be set via the :col-name
slot initarg. This value, which is not evaluated, will be passed to
to-sql-name.
Mention :col-name in the DAO docuemntation
Evaluate the arguments passed in via the s-sql:$$ placeholder with cl-postgres:to-sql-string
As per postgresql's convention if the conection host is a string which starts with #\/ connect to a unix socket in that diretory.

To simplify some of the #+ccl and #+sbcl and avoid some code duplication
usocket is always used when connecting to an inet socket.

The change only affects those connections whose host is a string or a
pathname, :unix as a host still works as before (and depends on the
conection time value of *unix-socket-dir*).
Added .gitignore
Merge remote-tracking branch 'upstream/master'

Conflicts:
	cl-postgres.asd
	cl-postgres/public.lisp

Simply take the contents as they are in upstream/master.