Add the initial sysctl implementation code.

(It's not yet linked into the build or in the exported symbols list.)
Add a local copy of the libnv from -HEAD.

This is used by the upcoming sysctl code to serialise data in and out.
Add a local version of memstat, to pull allocator data out of libuinet.
Add local copies of sysctl/vmstat, hacked up to (mostly) work within
libuinet.
Merge pull request #19 from erikarn/adrian_sysctl_prep

This is just the prep work - it doesn't include the build framework changes to build it, or the modifications to programs to call the sysctl setup path.