* util/i386/pc/grub-setup.c (setup): Rename prefix to

* util/i386/pc/grub-setup.c (setup): Rename prefix to
install_prefix, in line with install_dos_part and install_bsd_part.
Add new prefix variable, which is copied to install_prefix after
comparing core.img in memory with the one read from disk in the
no-embedding case, and use that rather than overwriting
install_prefix immediately when installing to a partition.
Fixes Debian bug #586621; based on patches by Matt Kraai and M. Vefa
Bicakci.