[NeoStats-Devel] ADNS library

The ADNS library was previously handled by separate versions for Win32 and
*nix. These have now been combined into a single library. This merge
identified an issue with differences in the libevent implementation so the
*nix one has been chosen as authoritative in this instance. 

There should be no operational changes from this merge but bugs may have
crept in during the merge so be aware of any oddities with ADNS.

The merged ADNS repeats a number of things that are handled by our new
oscalls API so I intend to migrate ADNS to use the NeoStats core for these
and other functions. Since ADNS appears to have gone some time without any
changes, I am also considering merging what remains of the library with the
main source code once this is completed.

Mark.