pgsql: psql: fix variable existence tab completion

psql: fix variable existence tab completion

psql has the :{?name} syntax for testing for a psql variable existence. This
commit implements a tab completion for this syntax. Notably, in order to
implement this we have to remove '{' from WORD_BREAKS. It appears that
'{' here from the very beginning and it comes from the default value of
rl_basic_word_break_characters. And :{?name} is the only psql syntax using
the '{' sign. So, removing it from WORD_BREAKS shouldn't break anything.

Discussion: https://postgr.es/m/CAGRrpzZU48F2oV3d8eDLr%3D4TU9xFH5Jt9ED%2BqU1%2BX91gMH68Sw%40mail.gmail.com
Author: Steve Chavez
Reviewed-by: Erik Wienhold

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/927332b95e778c0d15a9fbf96e3efeab0d3d937c

Modified Files
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src/bin/psql/t/010_tab_completion.pl | 8 ++++++++
src/bin/psql/tab-complete.c | 4 +++-
2 files changed, 11 insertions(+), 1 deletion(-)