Documentation bug: reference to checkpoint activity in bgwriter

ISTM that the following reference, at config.sgml line 1345, ought to
be adjusted due to the introduction of the new checkpointer process:

 Setting this to zero disables
         background writing (except for checkpoint activity).

--=20
Peter Geoghegan =A0 =A0 =A0 http://www.2ndQuadrant.com/
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