There was a problem when building from source where for example

@bindir@ would resolve to ${prefix}/bin.

This patch fixes it, based on http://www.gnu.org/software/autoconf/manual/
autoconf-2.69/html_node/Installation-Directory-Variables.html

It also changes opt_modulefiles_slurm to opt_modulefiles_slurm.in but
I couldn't figure out how to get git diff to show that.