Improve DLL search path fixer.

[rpavlik]

• Use a class to keep track of state.
• Use the Unity Application data dir property instead of current directory + "Assets"
• Handle looking in x86 vs x86_64 - does not fully fix the 64-bit support but it's one step.

@DuFF14 can you test this with Unity Pro and make sure it works, both in the editor and the compiled build player? It should solve the issue of looking in the wrong place in compiled builds.

[DuFF14]

It works, in the editor and the build!
I did get an error when opening Unity:

ArgumentException: get_dataPath can only be called from the main thread.
Constructors and field initializers will be executed from the loading thread when loading a scene.
Don't use this function in the constructor or field initializers, instead move initialization code to the Awake or Start function.
OSVR.Unity.DLLSearchPathFixer..ctor () (at Assets/OSVRUnity/src/DLLSearchPathFixer.cs:54)
OSVR.Unity.DLLSearchPathFixer.fix () (at Assets/OSVRUnity/src/DLLSearchPathFixer.cs:40)
OSVR.Unity.ClientKit..cctor () (at Assets/OSVRUnity/src/ClientKit.cs:83)
Rethrow as TypeInitializationException: An exception was thrown by the type initializer for OSVR.Unity.ClientKit

[rpavlik]

Oh rats, so that means either we can't use the data dir property, or we have to adjust where we're calling the fixer from.

[DuFF14]

Moving DLLSearchPathFixer.fix(); from the static constructor to the Awake() function makes the error go away and everything still works.