gitweb: get_file_owner and XML special characters

Hi,

I think current gitweb generates invalid XHTML when get_file_owner returns a 
string containing <>&.  (Version 1.5.2.1 certainly does, and in a quick browse 
of current source I didn't notice relevant changes.)

Here is a dirty patch to fix this problem.  Apologies if it is no longer a 
problem or if the patch is gross.
Thanks,
Eddie (newbie)