pgsql: Repair oversight in creation of "append relations": we should set

Log Message:
-----------
Repair oversight in creation of "append relations": we should set up
rel->tuples as well as rel->rows, since some estimation functions expect both
to be valid in every baserel. Per report from Dave Dutcher.

Tags:
----
REL8_2_STABLE

Modified Files:
--------------
pgsql/src/backend/optimizer/path:
allpaths.c (r1.154 -> r1.154.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/allpaths.c.diff?r1=1.154&r2=1.154.2.1)