[merge] doc: coding standards for repr methods

[Ian Clatworthy]

Ian Clatworthy has voted tweak.
Status is now: Conditionally approved
Comment:
As Michael suggested, the output from repr shouldn't be pages and pages 
long, so developers need to consider that for potentially large objects.
One extra sentence ought to cover that.

I wouldn't mind seeing a short NEWS item either, particularly mentioning 
the improvements to the PPA related processes.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3Ce01316480805270115k661872ccga198d2c0f69da777%40mail.gmail.com%3E