That's been there since Beta 1 and was mentioned in the WWDC keynote. A useful feature borrowed from the Google Photos app (I think).New Thing, i think :
If you select Photos in your Library or in your iCloud Library & Stream you can just drag you Finger over them and it will select them all where you swiped over it. I think this is new and it is really convenient. Before you had to tap them one by one i think.