If-Modified-Since is sent by http clients to be notified if a file has
been changed. This patch adds a function server_file_modified_since
that checks the time of the file from stat with the time sent from the
client. The separate function will help implement proper Range support.
I found 'timeoff
If-Modified-Since is already sent by most web browsers to httpd. This
patch adds a check to server_file_access before we send the file back.
This does not do any checks for autoindex directories as the size and
last modification dates of files would not get updated properly.
I separated the logic
