Made parser check for valid copy to/from stdin/stdout combinations.

src/interfaces/ecpg/test/expected/sql-desc.stderr

src/interfaces/ecpg/test/expected/sql-dynalloc.stderr

src/interfaces/ecpg/test/expected/sql-dynalloc2.stderr

src/interfaces/ecpg/test/expected/sql-dyntest.stderr

src/interfaces/ecpg/test/expected/sql-dyntest2.c

src/interfaces/ecpg/test/expected/sql-dyntest2.stderr

src/interfaces/ecpg/test/expected/sql-dyntest2.stdout

src/interfaces/ecpg/test/expected/sql-indicators.stderr

src/interfaces/ecpg/test/expected/sql-quote.stderr

src/interfaces/ecpg/test/expected/sql-show.stderr

src/interfaces/ecpg/test/pg_regress.inc.sh.in

src/interfaces/ecpg/test/pg_regress.sh

src/interfaces/ecpg/test/sql/dyntest2.pgc