Added just another compatibility level for Informix.

src/interfaces/ecpg/ChangeLog

src/interfaces/ecpg/ecpglib/connect.c

src/interfaces/ecpg/ecpglib/data.c

src/interfaces/ecpg/ecpglib/execute.c

src/interfaces/ecpg/ecpglib/extern.h

src/interfaces/ecpg/ecpglib/prepare.c

src/interfaces/ecpg/preproc/ecpg.c

src/interfaces/ecpg/preproc/extern.h

src/interfaces/ecpg/preproc/pgc.l

src/interfaces/ecpg/preproc/preproc.y

src/interfaces/ecpg/test/test_informix.pgc