Misleading messages say bootloader installs to MBR

Created an attachment (id=3809)
Fix the slightly misleading message for the installer.

usetup should provide "install boot loader to boot sector" as a choice, not MBR, since the MBR is the home of the code that boots the active partition's boot sector. See the attached patch for an alternate way of wording it; though all translations need to be updated, too.