Make JamPlus build correctly for linux64

Hi,

I just cloned the latest version of JamPlus and it wouldn't build for me for linux64 (i.e. make linux64). It seemed like there were a few files missing, and I also had a problem the -ldl linker flag was specified at the start of the commandline, whereas g++ seemed to want it at the end of the commandline.

I thought these changes might be of some use to you.
--
Jan