Use "R -f waverepo_installs.R" rather than Rscript.

When installing packages, sometimes the user could be asked to upgrade
old packages.  As the session was non-interactive, the user never got
to see this problem.  So, now by using an interactive session, the
user should see what is happening.

Problem found thanks to feedback from Phillip Lord.
Update install.package() call for sjemea.

Macs expect a .tgz (binary package) by default.  So tell it instead to
install from source.