The buildfarm doesn't like this, because some buildfarm members have
log_statement = 'all'.  We could change the log level of the messages
instead, but Tom doesn't like that.  So let's do this instead, at
least for now.

Patch by Sergei Kornilov, applied here in reverse.

Discussion: http://postgr.es/m/2123251552490241@myt6-fe24916a5562.qloud-c.yandex.net