implement mac OS X version of get desktop path

src/platform_osx.mm

@@ -1,7 +1,35 @@
 #include "config.h"
 
+#include <string>
+
+#import <Foundation/Foundation.h>
+
+static void ensure_trailing_slash(std::string& path)
+{
+	if (path.size() && path[path.size()-1] != '/') {
+		path += "/";
+	}
+}
+
+static std::string get_desktop_dir()
+{
+	std::string ret;
+	NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
+
+	NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDesktopDirectory, NSUserDomainMask, YES);
+	NSString *path = [paths objectAtIndex: 0];
+
+	ret = [path fileSystemRepresentation];
+
+	[pool drain];
+
+	ensure_trailing_slash(ret);
+	return ret;
+}
+
 
 void Config::setupPaths()
 {
-	
+	desktopPath = get_desktop_dir();
-}
+}
+