pgsql: Nab some low-hanging fruit: replace the planner's base_rel_list

Log Message:
-----------
Nab some low-hanging fruit: replace the planner's base_rel_list and
other_rel_list with a single array indexed by rangetable index.
This reduces find_base_rel from O(N) to O(1) without any real penalty.
While find_base_rel isn't one of the major bottlenecks in any profile
I've seen so far, it was starting to creep up on the radar screen
for complex queries --- so might as well fix it.

Modified Files:
--------------
pgsql/src/backend/nodes:
outfuncs.c (r1.253 -> r1.254)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/outfuncs.c.diff?r1=1.253&r2=1.254)
pgsql/src/backend/optimizer/path:
allpaths.c (r1.131 -> r1.132)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/allpaths.c.diff?r1=1.131&r2=1.132)
pgsql/src/backend/optimizer/plan:
planmain.c (r1.82 -> r1.83)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/planmain.c.diff?r1=1.82&r2=1.83)
pgsql/src/backend/optimizer/util:
relnode.c (r1.67 -> r1.68)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/relnode.c.diff?r1=1.67&r2=1.68)
pgsql/src/include/nodes:
relation.h (r1.110 -> r1.111)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/relation.h.diff?r1=1.110&r2=1.111)