Load libraries without the .so suffix to make it work in other OSes

[jmcarcell]

Should fix #338

BEGINRELEASENOTES

• Load libraries without the .so suffix to make it work in other OSes

ENDRELEASENOTES

[tmadlener]

I got a report that things work on mac OS with this.

[jmcarcell]

Ok I was going to test it but then I don't; it looks like this is how loading libraries is done in ROOT most of the time unless they are Linux-specific, and locally it works for me on Linux.

[tmadlener]

I also seem to remember documentation about this being the recommended way to do this for platform agnostic support, but I can't find that right now.

[jmcarcell]

There is this:
https://github.com/root-project/root/blob/e42b5a6379835e541e09e577879661c538e1968f/core/unix/src/TUnixSystem.cxx#L4803
that is telling us which suffixes are being used