Do not attempt to set contentSize for a keyboard-avoiding scroll view if autoLayout is used to manage the subviews.

if layout constraints are used to position subviews of a scrollview, then the contentSize will be derived from the layout constraints, and we should not be attempting to override it.
Merge pull request #64 from chucks/contentsize-autolayout

Do not attempt to set contentSize for a keyboard-avoiding scroll view if...