fixed parsing of Pg COMMENT ON ... syntax

fixed parsing of Pg COMMENT ON ... syntax

previously only recognised comments on TABLE and COLUMN
also would not recognise comment_phrases split over multiple lines

now accept all comment types; however, it does not add information
to the datamodel except for TABLE and COLUMN

accepts comments split over multiple lines

will barf if comment includes escaped singlequote ''

test 08 extended to deal with parsing comments gracefully
(does not check contents of datamodel however)