pgsql: Fix failure of contrib/auto_explain to print per-node timing inf

Fix failure of contrib/auto_explain to print per-node timing information.

This has been broken since commit af7914c6627bcf0b0ca614e9ce95d3f8056602bf,
which added the EXPLAIN (TIMING) option. Although that commit included
updates to auto_explain, they evidently weren't tested very carefully,
because the code failed to print node timings even when it should, due to
failure to set es.timing in the ExplainState struct. Reported off-list by
Neelakanth Nadgir of Salesforce.

In passing, clean up the documentation for auto_explain's options a
little bit, including re-ordering them into what seems to me a more
logical order.

Branch
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REL9_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/47288bd08c0169ecb5eb50742336cc0df813777e

Modified Files
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contrib/auto_explain/auto_explain.c | 5 +--
doc/src/sgml/auto-explain.sgml | 77 ++++++++++++++++++++---------------
2 files changed, 46 insertions(+), 36 deletions(-)