First stab at adding ngrep

I'm not sure what to call the licence; it seems to be the BSD licence
with a few clauses about attribution added (which I *think* we're
complying with)

This has only been tested on Yosemite.

I'm guessing this will need some tweaking (the name of the license at least) before it can land.
I prefer to grep for version too, like `$(SBinDir)/ngrep --version | grep $(Version)` It's a simple test (the binary is there? the correct version is printing?), but worths it.