[PATCH] Fix column SQL

attached patch fixes SQL of column in SQL pane.
sql should be like
ALTER TABLE table ADD COLUMN tms timestamp without time zone NOT NULL
DEFAULT now();
and not
ALTER TABLE table ADD COLUMN tms timestamp without time zone;
ALTER TABLE table ALTER COLUMN tms SET NOT NULL;
ALTER TABLE table ALTER COLUMN tms SET DEFAULT now();

it avoids not null constraint problem when you add column to existing
table with some data

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All bugs reserved