pgsql: pg_receivexlog: Rename option --dir to --directory

pg_receivexlog: Rename option --dir to --directory

getopt_long() allows abbreviating long options, so we might as well
give the option the full name, and users can abbreviate it how they
like.

Do some general polishing of the --help output at the same time.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/7d754961f799634128fb2d77632e2b53b736ae21

Modified Files
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doc/src/sgml/ref/pg_receivexlog.sgml | 2 +-
src/bin/pg_basebackup/pg_receivexlog.c | 17 ++++++++---------
2 files changed, 9 insertions(+), 10 deletions(-)