I added a port switch for postgresql in ob-sql.el

If you have sql loaded and do something like the follow:

#+name: example
#+header: :engine postgresql
#+header: :dbhost localhost
#+header: :dbport 6543
#+header: :dbuser orgmode
#+header: :database ob-sql
#+BEGIN_SRC sql
select * from everything
#+END_SRC

Note: default port for postrgres is 5432 not 6543

You will be either presented with an error or in my case a failed
password prompt since I had multiple db servers running. The problem was
that org-babel-sql-dbstring-postgresql did not accept a port argument.

I have attached a simple patch to fix this and have verified it works
for me. I would have loved to add some tests, but I ran into some
problems:

1) I could not figure out how to get just one test file to run
2) I was not able get make test to load the sql language in babel


Is there a recommended/standard way to resolve these problems with tests?