pgsql: Add unicode_{column|header|border}_style to psql

Add unicode_{column|header|border}_style to psql

With the unicode linestyle, this adds support to control if the
column, header, or border style should be single or double line
unicode characters.  The default remains 'single'.

In passing, clean up the border documentation and address some
minor formatting/spelling issues.

Pavel Stehule, with some additional changes by me.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/a2dabf0e1dda93c860b10bff7b73617e7b090108

Modified Files
--------------
doc/src/sgml/ref/psql-ref.sgml     |   40 +++++++--
src/bin/psql/command.c             |   96 +++++++++++++++++++++
src/bin/psql/help.c                |    3 +-
src/bin/psql/print.c               |  168 ++++++++++++++++++++++++++++++------
src/bin/psql/print.h               |   10 +++
src/bin/psql/startup.c             |    8 ++
src/bin/psql/tab-complete.c        |   13 ++-
src/test/regress/expected/psql.out |    3 +
8 files changed, 307 insertions(+), 34 deletions(-)