Avoid some compilation warnings and errors with gcc on linux.

src/console.cpp

@@ -162,5 +162,5 @@ void user_printf(const char *format, ...)
   uvsprintf(buf, format, ap);
   va_end(ap);
 
-  allegro_message(buf);
+  allegro_message("%s", buf);
 }

src/main.cpp

@@ -72,7 +72,7 @@ int vaca_main()
     e.show();
   }
   catch (std::exception& e) {
-    allegro_message(e.what());
+    allegro_message("%s", e.what());
   }
 #ifndef DEBUGMODE
   catch (...) {

src/resource_finder.cpp

@@ -19,6 +19,7 @@
 #include "config.h"
 
 #include <allegro.h>
+#include <cstdio>
 
 #include "resource_finder.h"