Thanks Tim - hadn't noticed it there. I was trying to use the 10.5 config in the main branch download.
I did have problems downloading the 10.5 branch though - just in case anyone else has this problem...on github, you go in and select the 10.5 branch, and click the Download Source button, choose the file format and then it says "Hardcore Archiving Action"...and just sits there forever, and you never get the download.
If you look at the URL it will say
http://waitdownload.github.com/... now if you wait a reasonable amount of time for it to zip the file (maybe half a minute) then change the url to be download instead of waitdownload, then you get your file.
I only have this problem on the branch - the normal download works just fine for me. YMMV. HTH.