crond: simplify logging code

crond: simplify logging code

Slight change in behavior: now -l 5 will enable the same messages
formerly only enabled for -d 5. (Old behavior was non-sensical).

function                                             old     new   delta
reopen_logfile_to_stderr                               -      34     +34
log8                                                   -      26     +26
log7                                                   -      26     +26
log5                                                   -      26     +26
load_crontab                                         706     688     -18
rescan_crontab_dir                                   157     137     -20
crond_main                                          1486    1456     -30
fork_job                                             389     343     -46
crondlog                                             108      38     -70
------------------------------------------------------------------------------
(add/remove: 4/0 grow/shrink: 0/5 up/down: 112/-184)          Total: -72 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>