pgsql: Rework option set of vacuumlo

Rework option set of vacuumlo

Like oid2name, vacuumlo has been lacking consistency with other
utilities for its options:
- Connection options gain long aliases.
- Document environment variables which could be used: PGHOST, PGPORT and
PGUSER.

Documentation and code is reordered to be more consistent. A basic set
of TAP tests has been added while on it.

Author: Tatsuro Yamada
Reviewed-by: Michael Paquier
Discussion: https://postgr.es/m/c7e7f25c-1747-cd0f-9335-390bc97b2db5@lab.ntt.co.jp

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/bfea331a5e1b993d22071fc1696e6e8811d2d0d4

Modified Files
--------------
contrib/vacuumlo/.gitignore     |  2 ++
contrib/vacuumlo/Makefile       |  6 ++++
contrib/vacuumlo/t/001_basic.pl |  9 +++++
contrib/vacuumlo/vacuumlo.c     | 79 ++++++++++++++++++++++++-----------------
doc/src/sgml/vacuumlo.sgml      | 39 +++++++++++++++++---
5 files changed, 98 insertions(+), 37 deletions(-)