Clean up possibly-uninitialized-variable warnings reported by gcc 4.x.

src/backend/access/nbtree/nbtinsert.c

src/backend/catalog/pg_proc.c

src/backend/commands/copy.c

src/backend/commands/functioncmds.c

src/backend/commands/tablecmds.c

src/backend/optimizer/path/indxpath.c

src/backend/optimizer/plan/createplan.c

src/backend/optimizer/plan/planner.c

src/backend/regex/rege_dfa.c

src/backend/regex/regexec.c

src/backend/utils/adt/inet_net_ntop.c

src/backend/utils/adt/nabstime.c

src/backend/utils/adt/selfuncs.c

src/backend/utils/cache/catcache.c

src/backend/utils/misc/guc.c

src/interfaces/ecpg/pgtypeslib/datetime.c

src/pl/plpgsql/src/pl_comp.c