pgsql-server: Repair some issues with column aliases and RowExpr

Log Message:
-----------
Repair some issues with column aliases and RowExpr construction in the
presence of dropped columns.  Document the already-presumed fact that
eref aliases in relation RTEs are supposed to have entries for dropped
columns; cause the user alias structs to have such entries too, so that
there's always a one-to-one mapping to the underlying physical attnums.
Adjust expandRTE() and related code to handle the case where a column
that is part of a JOIN has been dropped.  Generalize expandRTE()'s API
so that it can be used in a couple of places that formerly rolled their
own implementation of the same logic.  Fix ruleutils.c to suppress
display of aliases for columns that were dropped since the rule was made.

Modified Files:
--------------
    pgsql-server/src/backend/catalog:
        dependency.c (r1.36 -> r1.37)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/catalog/dependency.c.diff?r1=1.36&r2=1.37)
    pgsql-server/src/backend/optimizer/path:
        allpaths.c (r1.118 -> r1.119)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/optimizer/path/allpaths.c.diff?r1=1.118&r2=1.119)
    pgsql-server/src/backend/optimizer/prep:
        prepjointree.c (r1.20 -> r1.21)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/optimizer/prep/prepjointree.c.diff?r1=1.20&r2=1.21)
    pgsql-server/src/backend/optimizer/util:
        var.c (r1.59 -> r1.60)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/optimizer/util/var.c.diff?r1=1.59&r2=1.60)
    pgsql-server/src/backend/parser:
        parse_clause.c (r1.133 -> r1.134)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/parser/parse_clause.c.diff?r1=1.133&r2=1.134)
        parse_coerce.c (r2.120 -> r2.121)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/parser/parse_coerce.c.diff?r1=2.120&r2=2.121)
        parse_relation.c (r1.97 -> r1.98)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/parser/parse_relation.c.diff?r1=1.97&r2=1.98)
        parse_target.c (r1.122 -> r1.123)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/parser/parse_target.c.diff?r1=1.122&r2=1.123)
    pgsql-server/src/backend/rewrite:
        rewriteHandler.c (r1.141 -> r1.142)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/rewrite/rewriteHandler.c.diff?r1=1.141&r2=1.142)
        rewriteManip.c (r1.85 -> r1.86)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/rewrite/rewriteManip.c.diff?r1=1.85&r2=1.86)
    pgsql-server/src/backend/utils/adt:
        ruleutils.c (r1.177 -> r1.178)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/adt/ruleutils.c.diff?r1=1.177&r2=1.178)
    pgsql-server/src/include/nodes:
        parsenodes.h (r1.265 -> r1.266)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/nodes/parsenodes.h.diff?r1=1.265&r2=1.266)
        primnodes.h (r1.101 -> r1.102)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/nodes/primnodes.h.diff?r1=1.101&r2=1.102)
    pgsql-server/src/include/parser:
        parse_relation.h (r1.44 -> r1.45)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/parser/parse_relation.h.diff?r1=1.44&r2=1.45)
        parsetree.h (r1.25 -> r1.26)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/parser/parsetree.h.diff?r1=1.25&r2=1.26)
    pgsql-server/src/include/rewrite:
        rewriteManip.h (r1.35 -> r1.36)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/rewrite/rewriteManip.h.diff?r1=1.35&r2=1.36)