Git silently ignores --date when data is not in the correct format

Hi,

on 1.7.3.3, I have noticed that git --commit silently ignores the 
--date=<date> switch if <date> is not in the current format.

for instance

git --commit --amend --date="10.11.2010" creates a commit with the current
date and time, because the --date argument misses the time.

possibly, it would be better to stop with an error message.