Internalize node_version.h.

With the more detailed node.version changing (every commit), having
node_version.h exposed to all modules required a complete recompile each
time a commit was made.

People can use the javascript interface to get the version.

src/node.cc

@@ -22,6 +22,7 @@
 #include <node_stdio.h>
 #include <node_natives.h>
 #include <v8-debug.h>
+#include <node_version.h>
 
 using namespace v8;