caseFieldAccessors is an allocation hotspot

[retronym]

Rework this:

    /** For a case class, the symbols of the accessor methods, one for each
     *  argument in the first parameter list of the primary constructor.
     *  The empty list for all other classes.
     *
     * This list will be sorted to correspond to the declaration order
     * in the constructor parameter
     */
    final def caseFieldAccessors: List[Symbol] = {
      // We can't rely on the ordering of the case field accessors within decls --
      // handling of non-public parameters seems to change the order (see scala/bug#7035.)
      //
      // Luckily, the constrParamAccessors are still sorted properly, so sort the field-accessors using them
      // (need to undo name-mangling, including the sneaky trailing whitespace)
      //
      // The slightly more principled approach of using the paramss of the
      // primary constructor leads to cycles in, for example, pos/t5084.scala.
      val primaryNames = constrParamAccessors map (_.name.dropLocal)
      caseFieldAccessorsUnsorted.sortBy { acc =>
        primaryNames indexWhere { orig =>
          (acc.name == orig) || (acc.name startsWith (orig append "$"))
        }
      }
    }

To avoid the call to append inside the inner loop.