pgsql: Don't override arguments set via options with positional argumen

Don't override arguments set via options with positional arguments.

A number of utility programs were rather careless about paremeters
that can be set via both an option argument and a positional
argument. This leads to results which can violate the Principal
Of Least Astonishment. These changes refuse to use positional
arguments to override settings that have been made via positional
arguments. The changes are backpatched to all live branches.

Branch
------
REL8_4_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/095527a7019718f4c1f5206b2ac634d11903366d

Modified Files
--------------
src/bin/initdb/initdb.c | 7 +++++--
src/bin/scripts/clusterdb.c | 26 +++++++++++++++-----------
src/bin/scripts/createlang.c | 14 ++++++++++++--
src/bin/scripts/droplang.c | 14 ++++++++++++--
src/bin/scripts/reindexdb.c | 25 +++++++++++++++----------
src/bin/scripts/vacuumdb.c | 27 ++++++++++++++++-----------
6 files changed, 75 insertions(+), 38 deletions(-)