pgsql: Support optional FROM/IN in FETCH and MOVE The main motivation

Log Message:
-----------
Support optional FROM/IN in FETCH and MOVE

The main motivation for this is that it's required for Informix compatibility
in ECPG.

This patch makes the ECPG and core grammars a bit closer to one another for
these productions.

Author: Zoltan Boszormenyi

Modified Files:
--------------
    pgsql/src/backend/parser:
        gram.y (r2.690 -> r2.691)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y?r1=2.690&r2=2.691)
    pgsql/src/interfaces/ecpg/preproc:
        ecpg.addons (r1.6 -> r1.7)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/preproc/ecpg.addons?r1=1.6&r2=1.7)
    pgsql/src/interfaces/ecpg/test/expected:
        compat_informix-test_informix.c (r1.19 -> r1.20)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/expected/compat_informix-test_informix.c?r1=1.19&r2=1.20)
        compat_informix-test_informix.stderr (r1.15 -> r1.16)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/expected/compat_informix-test_informix.stderr?r1=1.15&r2=1.16)