[CMake] new rpath support

[Brad King]

Zachary Pincus wrote:
>> The solution on Windows is just to put the runtime DLLs in the same  
>> directory as the modules that need them.
> 
> Is this the case even if the modules aren't in the same directory as  
> the python executable? The python executable will be in one place,  and 
> the python module dlls will be in another, and the runtime dll  will be 
> in the same directory as the modules. The windows loader will  then know 
> to find the runtime in the directory that the modules are in?

When a module is loaded dynamically Windows will look in the directory 
containing the module for its runtime DLLs.  The location of the python 
executable does not matter in this case.

-Brad