UNIX agent Postgres versions

This issue is based on the mailing list thread with the same subject from 2016-01-05.
Below I included an excerpt of the posts:
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I was in the process of configuring the UNIX agent and I found (as written in the documentation too) that the script only supports Postgres version 9.
But after experimenting a little bit I realized that the script works perfectly with the 8.4 version. I was able to test with an 8.3 which was working as well.
So maybe the script should be changed to enable any 8.X version.
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Reading the documentation, I did find out that the tuples stats collection was added in version 8.3, so I changed my file (patch attached).
And indeed, testing on 8.3 and 8.4 everything works perfectly, it can find and extract every information, on an older server that has 8.1 installed, it simply doesn't aggregate tuples data.
I didn't put time in investigating older versions as they are really obsolete.

I didn't know which is the proper way to fix the output:

• output all zero values for the tuples stats
• don't output anything at all for nonexistent values
  so I decided I would go with the second choice. This is reflected in my patch.

I added a small remark in the header of the file to indicate the version peculiarities.
The web page should be updated as well
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