BUG: offset normalize option may not work in addition/subtraction
Closes problem found in #7375.
@jreback Is this for 0.15 (needs release note)?

its for 0.14.1 (trying to release in next day or 2). @jorisvandenbossche noticed it. 

that's why I wanted a separate PR (you can update an existing entry if you want, or new is ok too)
 Understood. Appreciate your review.
 can you add in the doc examples explicity (i am sure they overlap, but just to make sure), the ones right above this: http://pandas-docs.github.io/pandas-docs-travis/timeseries.html#parametric-offsets (e.g. the section where it uses normalize)
 OK, added doc description.
 ok ping on green
