Add function (actually an int4 and an int8 version) that generates

Add function (actually an int4 and an int8 version) that generates
a series of numbers, optionally using an explicit step size other
than the default value (one). Use function in the information_schema
to replace hard-wired knowledge of INDEX_MAX_KEYS. initdb forced due
to pg_proc change. Documentation update still needed -- will be
committed separately.