pgsql: Define a new, more extensible syntax for COPY options.

Log Message:
-----------
Define a new, more extensible syntax for COPY options.

This is intentionally similar to the recently revised syntax for EXPLAIN
options, ie, (name value, ...).  The old syntax is still supported for
backwards compatibility, but we intend that any options added in future
will be provided only in the new syntax.

Robert Haas, Emmanuel Cecchet

Modified Files:
--------------
    pgsql/doc/src/sgml/ref:
        copy.sgml (r1.91 -> r1.92)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/copy.sgml?r1=1.91&r2=1.92)
    pgsql/src/backend/commands:
        copy.c (r1.316 -> r1.317)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/copy.c?r1=1.316&r2=1.317)
        define.c (r1.105 -> r1.106)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/define.c?r1=1.105&r2=1.106)
    pgsql/src/backend/parser:
        gram.y (r2.677 -> r2.678)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y?r1=2.677&r2=2.678)
    pgsql/src/test/regress/expected:
        copy2.out (r1.27 -> r1.28)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/copy2.out?r1=1.27&r2=1.28)
    pgsql/src/test/regress/sql:
        copy2.sql (r1.18 -> r1.19)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/copy2.sql?r1=1.18&r2=1.19)