Linux alternatives for the Windows headers and PerformanceCounter. Some typedefs and #defines for the Linux build. Fixed GetDataDir.

net.h

@@ -1,6 +1,12 @@
 // Copyright (c) 2009 Satoshi Nakamoto
 // Distributed under the MIT/X11 software license, see the accompanying
 // file license.txt or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef __WXMSW__
+#define closesocket(s) close(s)
+#define INVALID_SOCKET (SOCKET)(~0)
+typedef u_int SOCKET;
+#endif
 
 class CMessageHeader;
 class CAddress;