Fix solution, correcting tests for OSX

All tests passes

```
$ uname -a
Darwin local 11.4.2 Darwin Kernel Version 11.4.2: Thu Aug 23 16:25:48 PDT 2012; root:xnu-1699.32.7~1/RELEASE_X86_64 x86_64
```



Remember libsodium.dylib should match the arch on the current mono and must be installed in /usr/local/lib/libsodium.dylib (for the moment)

To check that:

```
$ mono --version
Mono JIT compiler version 3.2.6 ((no/9b58377 Thu Jan 16 17:49:56 EST 2014)
Copyright (C) 2002-2012 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
	TLS:           normal
	SIGSEGV:       altstack
	Notification:  kqueue
	Architecture:  x86
	Disabled:      none
	Misc:          softdebug 
	LLVM:          yes(3.3svn-mono-(no/8bdedb5)
	GC:            sgen
```
libsodium lib should be the same:

```
$ lipo -info /usr/local/lib/libsodium.dylib 
Non-fat file: /usr/local/lib/libsodium.dylib is architecture: i386
```
![screen shot 2014-04-26 at 9 42 56 pm](https://cloud.githubusercontent.com/assets/303538/2810273/d38942e6-cdad-11e3-8858-601662f8e729.png)