that they can be different.  Clean up mkfs, simplifying specifying fs parameters,
remove some redundancy between fs and mkfs, and fix disk layout bugs. Call blocks
in the file system blocks instead of sectors.  Passes usertests for different
block sizes.

Currently, grep read()s into a buffer and then uses the buffer as a
string. Since there's no NUL-terminator, this can cause it to falsely
identify line breaks and matches from leftover data on earlier lines
and, if a line fills up the entire buffer, to read past the end of the
buffer.

Fix this by NUL-terminating any data returned by read().

Thanks to Keiichi Watanabe for the report.

Presumably because of the pre-loaded file system, the default RAM is
insufficient when running kernelmemfs

Commit 9aa0337d introduced a linker script for linking the kernel image,
but only changed the kernel target to use it.  kernelmemfs was still
using the old linker command line arguments, which weren't sufficient.

the day of reckoning has come for the debug port "Shutdown" hack.

instead of mucking with ACPI or using a new hack, the student will now write
sys_date() using the cmosgetdate() helper.

for bug reported by symingz@gmail.com and cs1100254@cse.iitd.ernet.in

copyuvm() should not allow new copied pages to inherit more
permissions than the original pages.

But check that mkfs.c is building with LP64

Search for an addr2line that supports elf32-i386.  Don't print the
path of addr2line as a side-effect of which.  Don't uselessly pipe
"grep '^ '" to addr2line's stdin.  Enable as many pretty-printing and
otherwise helpful options as possible (this makes the output *much*
more pleasant on modern addr2lines).

0 is not a system call (thanks to Peter Froehlich)