Correct calculation of number of inodes from density for small filesystems.
Add a '-n inodes' option so that the desired number of inodes can be
explicitly given - init needs this for mfs /dev, -i density is too crude.
on the command line with the -u, -g and -p options respectively.
The old malloc() replacement (and related functions) didn't work with
the libc get{pw,gr}nam() functions so it was removed and a separate
memory allocation function added that is only called to allocate the
space for the MFS file system.
Also use a table for the usage flags instead of multiple fprintf()'s
with "if (mfs)" checks sprinkled through.
dsl