fixed up graylog2 installation for centos/scientific linux

this works on SL6.4 now, and works well. I also deleted the extraneous commenting, and put the bash script in -x mode which will beef up the output and make that commenting obsolete.

if you don't like the commits, i can certainly just keep this forked in my own repo. but I install graylog quite often, and this is a wonderful find, and i don't mind updating it as things break because of new releases etc.

cheers!