Try to detect when EIO_custom changed it's signature.

Should also be a part of #115 and #120.

src/Canvas.cc

@@ -133,7 +133,11 @@ toBuffer(void *c, const uint8_t *data, unsigned len) {
  * EIO toBuffer callback.
  */
 
+#if NODE_VERSION_AT_LEAST(0, 5, 4)
+void
+#else
 int
+#endif
 Canvas::EIO_ToBuffer(eio_req *req) {
   closure_t *closure = (closure_t *) req->data;
 
@@ -142,7 +146,9 @@ Canvas::EIO_ToBuffer(eio_req *req) {
     , toBuffer
     , closure);
 
+#if !NODE_VERSION_AT_LEAST(0, 5, 4)
   return 0;
+#endif
 }
 
 /*

src/Canvas.h

@@ -11,6 +11,7 @@
 #include <v8.h>
 #include <node.h>
 #include <node_object_wrap.h>
+#include <node_version.h>
 #include <cairo.h>
 
 using namespace v8;
@@ -43,7 +44,13 @@ class Canvas: public node::ObjectWrap {
     static void SetHeight(Local<String> prop, Local<Value> val, const AccessorInfo &info);
     static Handle<Value> StreamPNGSync(const Arguments &args);
     static Local<Value> Error(cairo_status_t status);
-    static int EIO_ToBuffer(eio_req *req);
+    static
+#if NODE_VERSION_AT_LEAST(0, 5, 4)
+      void
+#else
+      int
+#endif
+      EIO_ToBuffer(eio_req *req);
     static int EIO_AfterToBuffer(eio_req *req);
     inline cairo_surface_t *surface(){ return _surface; }
     inline uint8_t *data(){ return cairo_image_surface_get_data(_surface); }