Forms 1.5.0 breaks 1.4's support for iOS 6.1

Looks like 1.5 has broken 1.4's support for iOS 6.1 (6.1 support is documented on the Forms requirements page).

With a ListView.HasUnevenRows = true, I now get this exception:

[UITableView setEstimatedRowHeight:]: unrecognized selector sent to instance

with call stack:

UIKit_UITableView_set_EstimatedRowHeight_System_nfloat + 120
Xamarin_Forms_Platform_iOS_ListViewRenderer_UpdateEstimatedRowHeight + 1184

Xamarin_Forms_Platform_iOS_ListViewRenderer_OnElementChanged_Xamarin_Forms_Platform_iOS_ElementChangedEventArgs_1_Xamarin_Forms_ListView + 4340