Compilation errors fixed (from pid and fork).
Merge branch 'master' of github.com:y88huang/CS350-F13
Merge branch 'master' of github.com:y88huang/CS350-F13
Merge branch 'master' of github.com:y88huang/CS350-F13
Merge branch 'master' of github.com:y88huang/CS350-F13
Merge branch 'master' of github.com:y88huang/CS350-F13
Merge branch 'master' of github.com:y88huang/CS350-F13
More work on fork and pid. Now compiles.