More accurate build and install requirements

I found that, during the configure step, we're depending on
at least the presence of three packages above and beyond a
vanilla CentOS install and the development tools. I've
therefore omitted the development tools as well, as per
modern packaging guidelines. See https://fedoraproject.org/wiki/How_to_create_an_RPM_package#SPEC_file_overview
for more information.
Merge pull request #305 from emilyst/patch-1

More accurate build and install requirements