pgsql: Changed the way symbols are defined in C in INFORMIX mode.

Log Message:
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Changed the way symbols are defined in C in INFORMIX mode.
Added SQLSTATE macro closing bug #3961.
EXECUTE can return NOT FOUND so it should be checked here too.

Tags:
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REL8_3_STABLE

Modified Files:
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    pgsql/src/interfaces/ecpg:
        ChangeLog (r1.370 -> r1.370.2.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ChangeLog?r1=1.370&r2=1.370.2.1)
    pgsql/src/interfaces/ecpg/include:
        datetime.h (r1.12 -> r1.12.4.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/include/datetime.h?r1=1.12&r2=1.12.4.1)
        decimal.h (r1.14 -> r1.14.4.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/include/decimal.h?r1=1.14&r2=1.14.4.1)
        ecpg_informix.h (r1.18 -> r1.18.4.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/include/ecpg_informix.h?r1=1.18&r2=1.18.4.1)
        ecpglib.h (r1.74 -> r1.74.2.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/include/ecpglib.h?r1=1.74&r2=1.74.2.1)
    pgsql/src/interfaces/ecpg/preproc:
        pgc.l (r1.159 -> r1.159.2.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/preproc/pgc.l?r1=1.159&r2=1.159.2.1)
        preproc.y (r1.359 -> r1.359.2.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/preproc/preproc.y?r1=1.359&r2=1.359.2.1)