Re: COPY-able csv log outputs

The attached patch fixes all the issues I found in the original version of
this code and completes the review I wanted to do. Someone else will need
to take this from here. As I already mentioned, I can't comment on the
quality of the piping implementation used to add this feature other than
to say it worked for me.

Here is a sample line generated by the current code that illustrates most
of what I adjusted:

2007-05-28 13:45:14.028 EDT,"postgres","pgbench",465b1519.5f3d,laptop:32783,24381,17,idle,2007-05-28
13:44:57 EDT,60337,LOG,,"statement: select * from branches;"

In addition to cleanup and bug fixes, notable changes made from the
original version include:

-Changed connection information to standard host:port syntax

-Added a per process line number to allow a unique index. The code that
supports that in the current logs is very local to log_line_prefix.
Rather than try to share that information like is done for the timestamp,
it seemed easier to just duplicate those few lines of code for the CSV
output path. This could cause the CVS logs to have different values for
the line number of a statement than the text format ones. I didn't feel
that was a problem serious enough to justify the code refactoring that
would be required to assure the line numbers were identical.

-Added a new documentation section to the logging chapter devoted just to
the csvlog feature. It gives a sample table and import syntax. I also
gave recommendations on how to configure some related log file parameters
that can interact badly with this feature. For example, I noticed that if
log_rotation_size was set to a value, it could split the CSV lines in two;
the result was two CVS files you couldn't import because of the partial
lines in each. Since the rotation size feature causes other issues anyway
that make importing more complicated, documenting the issue seemed
sufficient.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD