pgsql: Allow CREATE TABLE (LIKE ...) from composite type

Allow CREATE TABLE (LIKE ...) from composite type

The only reason this didn't work before was that parserOpenTable()
rejects composite types. So use relation_openrv() directly and
manually do the errposition() setup that parserOpenTable() does.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/b59ca98209d45f5689fe9de22a7429d4cf09d40c

Modified Files
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doc/src/sgml/ref/create_table.sgml | 2 +-
src/backend/parser/parse_utilcmd.c | 34 +++++++++++++++++------
src/test/regress/expected/create_table_like.out | 14 +++++----
src/test/regress/sql/create_table_like.sql | 4 ++-
4 files changed, 37 insertions(+), 17 deletions(-)