Reverted project files back to use default nuget targets path.

Visual Studio has an annoying habit of reverting your hand-crafted modification to it's nuget target import line. Obviously in it's arrogance Visual Studio doesn't think I made that change on purpose so it would compile on \*nix boxes *not* confirming to Linux 1.0 Specification that states multiple forward-slashes in paths should be resolved to singular (e.g. `/var/something//me` --> `/var/something/me`).

As xbuild doesn't support property functions this commit is an alternative hack that seems to satisfy the Visual Studio ***"look ma it's really there"*-check** whilst allowing an additional import with condition for *nix boxes.