Fixed bug in %s handling.

src/interfaces/ecpg/ChangeLog

src/interfaces/ecpg/pgtypeslib/dt_common.c

src/interfaces/ecpg/test/expected/pgtypeslib-dt_test.c

src/interfaces/ecpg/test/expected/pgtypeslib-dt_test.stderr

src/interfaces/ecpg/test/expected/pgtypeslib-dt_test.stdout

src/interfaces/ecpg/test/pgtypeslib/dt_test.pgc