small performance fix for Array#add and docs.
small performance fix for Array#add and docs.


Former-commit-id: 92f17824c19f94d4316854203f79efa1dab0cc2a [formerly b984e709cafe38fea4eabff3f4bbe5dc50cd78aa]
Former-commit-id: 922f7b849498628f02b0aa3c6fe50b8b5507bd1f
andrewplummer/Sugar,romancow/Sugar,andrewplummer/Sugar,romancow/Sugar