Fixed "-auth guess" for LightDM/Ubuntu.

To fix the  

/tmp/fd.4zomKO: 305: [: -a: unexpected operator

error that occurs when trying  to use "-auth guess" on Ubuntu, I removed the extra space before "-auth" in the sed regexp for FindDisplay, which was causing the sed command to fail to match on Ubuntu.  That failure then made xa null and that made line 305 \" if [ -f $xa -a -r $xa ]; then \" choke, giving the above error message.