Bug #172 - add support for GUC "application_name" on PG versions that support this...

Bug #172 - add support for GUC "application_name" on PG versions that support this (e.g. - 9.0+)

Squashed commit of the following:

commit 2966ae0488067b72aa02f29b1bdeb60b84dc1a4d
Author: Christopher Browne <cbbrowne@ca.afilias.info>
Date:   Wed Dec 15 15:37:52 2010 -0500

    Need to free PG connection when done

commit 766acf3e105644878e19af8c1fa14f568f187341
Author: Christopher Browne <cbbrowne@ca.afilias.info>
Date:   Fri Dec 10 14:43:36 2010 -0500

    Revise slonik handling of application_name...

    Query to see if the GUC is there, and only try to set the GUC if it
    actually exists in this database.

commit bbe9a3f0f7015768bf3fbc044d9a9bf14039859f
Author: Christopher Browne <cbbrowne@ca.afilias.info>
Date:   Fri Dec 10 11:36:37 2010 -0500

    Add setting of application_name GUC to slonik

commit a2d97d94017e74b0fdad100f4be3b2327a56b29d
Author: Christopher Browne <cbbrowne@ca.afilias.info>
Date:   Fri Dec 10 11:23:32 2010 -0500

    Bug #172 - function to optionally set application_name, and usage of this for slon connections