Cleanly separate GUI socket-related code from net library.

This fixes linking problems under Unix introduced by recent changes which
fixed previous problems which were due to files not being linked in at all.

In order to provide a clean separation between base, net and core libraries we
now use the same wxSocketManager (wxSocketFDBasedManager), defined in net
library for both console and GUI Unix applications and just use different FD
IO manager for them: the latter can be defined in base and core libraries as
it doesn't involve wxSocketImpl at all, only its base wxFDIOHandler class.

At more detailed level, these changes required:
 1. Adding the new wxFDIOManager class.
 2. Refactoring the old (and now removed) wxSocketFDIOManager to use the same
    code as wxSocketFDIOManager. This involved:
  a) Adding handler and direction parameter to RemoveInput().
  b) Storing the mask of registered events in wxFDIOHandler itself.
  c) Defining wxFDIOManagerUnix which works with wxFDIODispatcher.
 3. Changing the traits classes in Unix ports to define GetFDIOManager()
    instead of GetSocketManager().

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61688 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/unix/apptrait.h

@@ -36,7 +36,12 @@ public:
 // TODO: Should we use XtAddInput() for wxX11 too? Or, vice versa, if there is
 //       no advantage in doing this compared to the generic way currently used
 //       by wxX11, should we continue to use GTK/Motif-specific stuff?
-#if defined(__WXGTK__) || defined(__WXMOTIF__) || defined(__WXMAC__)
+#if defined(__WXGTK__) || defined(__WXMOTIF__)
+    #define wxHAS_GUI_FDIOMANAGER
+    #define wxHAS_GUI_PROCESS_CALLBACKS
+#endif // ports using wxFDIOManager
+
+#if defined(__WXMAC__)
     #define wxHAS_GUI_PROCESS_CALLBACKS
     #define wxHAS_GUI_SOCKET_MANAGER
 #endif
@@ -76,9 +81,17 @@ public:
     virtual bool ShowAssertDialog(const wxString& msg);
 #endif
 
-#if wxUSE_SOCKETS && defined(wxHAS_GUI_SOCKET_MANAGER)
+#if wxUSE_SOCKETS
+
+#ifdef wxHAS_GUI_SOCKET_MANAGER
     virtual wxSocketManager *GetSocketManager();
 #endif
+
+#ifdef wxHAS_GUI_FDIOMANAGER
+    virtual wxFDIOManager *GetFDIOManager();
+#endif
+
+#endif // wxUSE_SOCKETS
 };
 
 #endif // wxUSE_GUI