Improve text quality of UI on Windows

When using the default pangocairo backend (win32),
AA is not enabled.

Switching to the FontConfig backend fixes the problem.

app/main.c

@@ -601,6 +601,9 @@ main (int    argc,
   gimp_init_signal_handlers (&backtrace_file);
 
 #ifdef G_OS_WIN32
+  /* Enable Anti-Aliasing*/
+  g_setenv ("PANGOCAIRO_BACKEND", "fc", TRUE);
+
   /* Reduce risks */
   SetDllDirectoryW (L"");