Broaden the filter for wallpaper restore

Tweak the filter parameters so that we now use any restored wallpaper image
that is larger than our ideal size, and will reject any smaller images only
if they are *much* smaller than our ideal size.  The specific threshold used
here will just barely reject Nexus One or Droid sized wallpapers for restore
onto a Xoom, but will pass anything larger.

Bug 4070129

Change-Id: I889bdb3ef5011343b2fccb2f81c6abc2f4603ee2