return a RowList with the rows included from scope by the fromx and wherex.
  When the scope has more than one name in it, the output will be a list of composite row
    (i.e. a row whose field types are themselves RowType).

def wherex_to_rowlist(scope_, fromx, wherex):
  """return a RowList with the rows included from scope by the fromx and wherex.
  When the scope has more than one name in it, the output will be a list of composite row
    (i.e. a row whose field types are themselves RowType).
  """
  single, multi = classify_wherex(scope_, fromx, wherex)
  single_rowlists = {
    tablename: table_to_rowlist(scope_[tablename], conds)
    for tablename, conds in misc.multimap(single).items() # i.e. {cond.table:[cond.exp, ...]}
  }
  raise NotImplementedError