Add code to the boot blocks to allow the user to place default boot strings
on block 1 of the disk (2nd block), should the correct magic numbers be present.
If the correct options are used it will 'delete' the name used from block1,
thereby assuring that if the boot fails it won't be stuck in an infinite loop.
the boot strings are set by the utility "nextboot"
(not yet checked in, but being tested.)
By default these changes should have no effect on existing installations
and if compiled without the NAMEBLOCK option should be essentially identical
to the old ones.
hd essentially wired the FreeBSD drive number to 0 without changing
the BIOS drive number. Now the numbers can be specified independently.
Replaced the BOOT_HD compile time flag with with BOOT_HD_BIAS. Defining
the new flag as 1 should give the same behaviour as defining the old
flag as anything. I haven't tested defining these flags.
