code: def print_package_versions(self):
          
          variants = self.context.get_tool_variants(self.tool_name)
          if variants:
              if len(variants) > 1:
                  self._print_conflicting(variants)
                  return 1
              else:
                  from rez.packages_ import iter_packages
                  variant = iter(variants).next()
                  it = iter_packages(name=variant.name)
                  rows = []
                  colors = []
  
                  for pkg in sorted(it, key=lambda x: x.version, reverse=True):
                      if pkg.version == variant.version:
                          name = "* %s" % pkg.qualified_name
                          col = heading
                      else:
                          name = "  %s" % pkg.qualified_name
                          col = local if pkg.is_local else None
  
                      label = "(local)" if pkg.is_local else ""
                      rows.append((name, pkg.path, label))
                      colors.append(col)
  
                  _pr = Printer()
                  for col, line in zip(colors, columnise(rows)):
                      _pr(line, col)
          return 0
docs: Print a list of versions of the package this tool comes from, and
          indicate which version this tool is from.