buffer: fix gcc 4.2 build breakage

gcc 4.2 on OS X gets confused about the call to node::Buffer::Data().
Fully qualify the function name to help it along.

Fixes the following build error:

    ../../deps/v8/include/v8.h: In function ‘char*
    node::Buffer::Data(v8::Handle<v8::Value>)’:
    ../../deps/v8/include/v8.h:900: error: ‘class v8::Data’
    is not a function,
    ../../src/node_buffer.h:38: error:
    conflict with ‘char* node::Buffer::Data(v8::Handle<v8::Object>)’
    ../../src/node_buffer.cc:94: error:
    in call to ‘Data’

src/node_buffer.cc

@@ -91,7 +91,9 @@ bool HasInstance(Handle<Object> obj) {
 
 char* Data(Handle<Value> val) {
   assert(val->IsObject());
-  return Data(val.As<Object>());
+  // Use a fully qualified name here to work around a bug in gcc 4.2.
+  // It mistakes an unadorned call to Data() for the v8::String::Data type.
+  return node::Buffer::Data(val.As<Object>());
 }