Modifications towards making code compile on win

Modifications to make code compile on windows

It should compile with win32, but for several reasons does not yet work on my 64bit win8: I did not yet manage to get cppunit build 64bit code and also we are triggering a VC++ compiler bug in "Realse" mode. In "Debug" mode things should build as the bug is related to optimization routines.

Further changes following
I encountered errors of the kind
```
Error	24	error C2491: 'nix::util::convertToSeconds' : definition of dllimport function not allowed	C:\Users\B\opt\nix\include\nix\util\util.hpp	118	1	TestRunner
```
which I had traced back to ```NIXEXPORT``` not being set. The way [Platform.hpp](https://github.com/G-Node/nix/blob/master/include/nix/Platform.hpp) is currently implemented the ```NIXAPI``` macro will either be ```__declspec(dllimport)``` if ```NIXEXPORT``` is not set, which I recon is the intended use. I did not trace the whole issue back but thought disabling import (by enabling export) would do for the ```TestRunner```.

Now having had a closer look indeed the issue is caused by 4 templated functions that use ```NIXAPI```. Since they are templated we cannot separate body and declaration into cpp and hpp but on the other hand import is not permitted on definitions but only on declarations.

So basically we are back at your other remark that export might be unnecessary on templated functions. :)