DLLSearchPathFixer on non-Windows platforms

[rpavlik]

Not sure how Mono assemblies handle search paths to native shared libraries on non-Windows (handled already) and non-iOS (static linking mandated) platforms like Mac or Android, possibly something RPATH-like. If it can't be built into the library like RPATH can, we'll need a similar functionality as found in DLLSearchPathFixer.cs (whose behavior is directly inspired by as close as an official Unity statement as I could find on the matter) so that not just the directly p/invoke accessed shared libraries, but also their dependencies, can be loaded.

The alternative would be special monolithic (single native shared library) builds of OSVR ClientKit, which might be a bit of a pain to get into the build system but could make life easier.

See:

• http://wiki.unity3d.com/index.php/Special_Folder_Names_in_your_Assets_Folder#.22Plugins.2Fx86_64.22
• http://forum.unity3d.com/threads/dllnotfoundexception-when-depend-on-another-dll.31083/#post-1042180

[rpavlik]

Doesn't appear to be affecting Android.