Collapsed four sequencetools functions.

    * sequencetools.negate_elements()
    * sequencetools.negate_elements_cyclically()
    * sequencetools.negate_absolute_value_of_elements_at_indices()
    * sequencetools.negate_absolute_value_of_elements_cyclically()

Use sequencetools.negate_elements() for everything.

CHANGE: should be included in the 2.15 change log.