fix FunctionCallbackInfo ambiguity

- when compiling tools that embed v8 with g++ FunctionCallbackInfo is currently ambigous
- more info: https://github.com/joyent/node/issues/7337
- original patch is here: https://codereview.appspot.com/78770045/

TBR=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/201573012

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20217 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8.h

@@ -133,6 +133,7 @@ template<class T, class P> class WeakCallbackObject;
 class FunctionTemplate;
 class ObjectTemplate;
 class Data;
+template<typename T> class FunctionCallbackInfo;
 template<typename T> class PropertyCallbackInfo;
 class StackTrace;
 class StackFrame;