Fix several bugs involving the obsolescent -d and -t options:
-d 0 and -t 0 were ignored
-t -600 was a usage error
-d 'atoi is not suitable for parsing args' and -t duh were not usage errors
Change some error messages to say which call to settimeofday failed.
Restore casts of NULL in function calls.
Finish conversion to using err() instead of perror().
