initial pass at EL setup

Mostly working, except Fedora at this stage because the RPMs aren't ready yet.

Complicating factors are that we need to know dist type ("el" or "fc"), version (5, 6, 7, 19, 20) and arch (i386, x86_64) with some special behaviour for each one. Fedora needs a little bit of special handling, EL5 needs special handling because it relies on EPEL and we have to check for existing installs of nodejs and npm because the clash is pretty ugly when you try and install.

The good news is that it works so far on EL 5, 6 and 7, both 64bit and 32bit, even the test script works which does a native addon compile (you need dev tools for that). Tested RedHat and CentOS.