pgsql: doc: Move ALTER TABLE IF EXISTS description to better place

doc: Move ALTER TABLE IF EXISTS description to better place

It was previously mixed in with the description of ALTER TABLE
subcommands.  Move it to the Parameters section, which is where it is on
other reference pages.

pointed out by Amit Langote

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/d64a9c8c833c497a926208c7ca898e270ecc6990

Modified Files
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doc/src/sgml/ref/alter_table.sgml |   20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)