Fix removing multiple system keys shortcuts.

Whenever users try to remove the system keys shortcuts, the
configuration file is overwritten and only records the last erase.

For example, if we wish to remove all the auto{A,B,L,R} keys at once,
we get the following writes on the configuration file:

NOOP=ALT+1,ALT+2,ALT+3,ALT+4
NOOP=ALT+2,ALT+3,ALT+4
NOOP=ALT+3,ALT+4
NOOP=ALT+4

Only `NOOP=ALT+4` stays for the following execution.

src/wx/opts.cpp

@@ -762,9 +762,11 @@ void update_opts()
     if (gopts.accels.size())
         cfg->SetPath(wxT("/Keyboard"));
 
+    int cmd_id = -1;
     for (wxAcceleratorEntry_v::iterator i = gopts.accels.begin();
          i < gopts.accels.end(); ++i) {
-        int cmd_id = i->GetCommand();
+        if (cmd_id == i->GetCommand()) continue;
+        cmd_id = i->GetCommand();
         int cmd;
 
         for (cmd = 0; cmd < ncmds; cmd++)