pgsql: Teach psql to do tab completion for names of psql variables.

Teach psql to do tab completion for names of psql variables.

Completion is supported in the context of \set and when interpolating
a variable value using :foo etc.

In passing, fix some places in tab-complete.c that weren't following
project style for comment formatting.

Pavel Stehule, reviewed by Itagaki Takahiro

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=b48b9cb3a46d80401b122fd10780e8c623983a26

Modified Files
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src/bin/psql/tab-complete.c |  197 +++++++++++++++++++++++++++++--------------
1 files changed, 134 insertions(+), 63 deletions(-)