Update date format between auth.log and linux system date

I noticed a problem with date format on /var/log/auth.log (tested on debian and ubuntu)

$ date '+%b %d'
Jun 09

/var/log/auth.log
Jun  9 13:17:01

So    grep "`date '+%b %d'`"    can't works fine for day with 1 digit.

I suggest to factorize and change the grep's regex with my update.
Merge pull request #322 from wh6b/patch-1

Update date format between auth.log and linux system date