In Release 58 of grub2 (and in every other distro I have looked at) the directory i386-pc is in /boot/grub2/ In Release 59 it is in /usr/lib, but not in /boot/grub2. This may have been intended, but as it stands, the bootloader cannot find core.img
Gee, that was service! I had no sooner filed this bug report, and the fix was waiting.
Status: NEW => RESOLVEDResolution: (none) => FIXED