Vector: Restore page-fade.png as fallback background-image for IE 6-9

Also corrects linear-gradient stop for main background from 40% to 50%
to match page-fade.png previously used.

Bug: 60991
Bug: 60943
Change-Id: I5cab42ee67bc1bb7dff01a7e51a2f609c96e0b18
Merge "Vector: Restore page-fade.png as fallback background-image for IE 6-9"