Minor fixes in to mailman 2 re. courier-to-mailman.py

The contributed (by me) file in mailman-2.1.14 contrib/courier-to-mailman.py is written to be auto-configured with proper path names by the configure script, a task which must be done manually if not done automatically in configure. This should be done just as it is for the qmail-to-mailman.py script which is properly re-written and deposited in the build subdir.

The attached patch will modify configure and configure.in appropriately so that this happens (only a mod to configure.in is required if autoconf is to be rerun).

This patch also fixes a minor spelling error in contrib/README.courier_to_mailman. Run patch with -p0

I understand that courier-MTA is a relatively little-known MTA, as compared to qmail. Courier is nonetheless a highly regarded full-featured MTA, is under active developent, fully GPL licensed, and has an active worldwide online support community. Qmail has a much larger installed base, but is relatively ancient in design and is almost entirely unsupported by the author. Most qmail installations these days are legacy installations.

If courier-to-mailman.py is to be included in the Mailman 2 distribution, please fully support it by allowing it to be fully set up by the Mailman configure script.