(PUP-2657) FFI Puppet::Util::Windows::Error

 - Remove dependency on 'windows/error'
 - Expand FFI helper methods from MemoryPointer to Pointer as we need
   them to operate on a chunk of memory that will be LocalFree'd (i.e.
   MemoryPointer is set to own the memory and autorelease when done)
 - Unfortunately, attempts to use FFI to call GetLastError were futile.
   FFI.errno should automatically be capturing the GetLastError result
   of any call made through FFI, however this doesn't appear to be the
   case in practice.  Furthermore, attempting to define GetLastError as
   a function in FFI yields the same result.  A number of tests fail
   as the error code is being stomped / swallowed.  The solution is to
   use Win32API.new to define / use this single function.  Sigh.