In order to enable the 'nachos -t' option for testing performance in
part 3 of homework 4, you will need to add '-DNACHOS_FS' to the DEFINES
line of the Makefile in the filesys directory. That is, change the 7th
line of the Makefile to:
DEFINES = -DFILE_SYS -DDISK -DCHANGED -DNACHOS_FS