Application name patch - v2

I believe the attached patch is ready for review at the next
commitfest. It does the following:

- Adds a userset GUC called application_name.
- Allows application_name to be reported in log_line_prefix using %a.
- Includes application_name in CSV logs.
- Displays application_name in the output of pg_stat_activity and
pg_stat_get_activity().
- Adds a PQconnectdb connection string option called application_name
and corresponding envvar PGAPPLICATIONNAME to allow application_name
to be set during connection.
- Adds a PQconnectdb connection string option called
fallback_application_name to allow applications to specify a default
application_name value that can be overriden by PGAPPLICATIONNAME.
- Ensures that the application_name value is processed early in the
connection phase to ensure it can be used in connection log messages.
- Includes docs

I think that covers all the suggestions discussed over the last couple
of days, with the exception of the rejection of \n and similar
characters which I'm still not entirely convinced is worth the effort.
Any other opinions on that? Anything else that should be
added/changed?

--
Dave Page
EnterpriseDB UK:   http://www.enterprisedb.com