Make number of args to a function configurable.

src/backend/access/hash/hashfunc.c

src/backend/access/nbtree/nbtcompare.c

src/backend/catalog/pg_aggregate.c

src/backend/catalog/pg_operator.c

src/backend/catalog/pg_proc.c

src/backend/catalog/pg_type.c

src/backend/commands/_deadcode/recipe.c

src/backend/commands/comment.c

src/backend/commands/indexcmds.c

src/backend/commands/proclang.c

src/backend/commands/remove.c

src/backend/commands/trigger.c

src/backend/executor/execQual.c

src/backend/libpq/be-pqexec.c

src/backend/parser/parse_coerce.c

src/backend/parser/parse_func.c

src/backend/parser/parse_target.c

src/backend/tcop/fastpath.c

src/backend/utils/adt/regproc.c

src/backend/utils/adt/selfuncs.c