log_error_verbosity placement

I just realized that log_error_verbosity is in the wrong section in
postgresql.conf and in our manual.  It is listed under "When to log"
when in fact it should be in the "What to log" section.

I also added documentation of what "terse" mode actually does.  I added
"verbosity" information a few weeks ago.

Patch attached.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +