psqldef: error occurs if cast in check constraint

[bubusuke]

Hi I fixed parse in check constraint.

A Parse error will occur if the CHECK constraint contains CAST as shown below.

    CREATE TABLE test (
      col text NOT NULL CHECK (col <> ''::text)
    );

error is.

found syntax error when parsing DDL "CREATE TABLE test (
          col text NOT NULL CHECK (col <> ''::text)
        )": syntax error at position 63 near 'text'

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I think the cause is insufficient CAST support when parsing Value.

[k0kubun]

merged #220. thanks!