Fixed parser and library to allow empty database names.

src/interfaces/ecpg/ChangeLog

src/interfaces/ecpg/ecpglib/connect.c

src/interfaces/ecpg/preproc/preproc.y

src/interfaces/ecpg/test/connect/test1.pgc.in

src/interfaces/ecpg/test/connect/test5.pgc

src/interfaces/ecpg/test/expected/compat_informix-dec_test.c

src/interfaces/ecpg/test/expected/compat_informix-rnull.c

...rfaces/ecpg/test/expected/compat_informix-test_informix.c

...faces/ecpg/test/expected/compat_informix-test_informix2.c

src/interfaces/ecpg/test/expected/complex-test1.c

src/interfaces/ecpg/test/expected/complex-test2.c

src/interfaces/ecpg/test/expected/complex-test3.c

src/interfaces/ecpg/test/expected/complex-test4.c

src/interfaces/ecpg/test/expected/complex-test5.c

src/interfaces/ecpg/test/expected/connect-test1.c

src/interfaces/ecpg/test/expected/connect-test1.stderr

src/interfaces/ecpg/test/expected/connect-test2.c

src/interfaces/ecpg/test/expected/connect-test3.c

src/interfaces/ecpg/test/expected/connect-test4.c

src/interfaces/ecpg/test/expected/connect-test5.c