added dependency on having protoheaders installed

turbo-rpc/SConscript

@@ -43,6 +43,7 @@ for file in proto_files:
 # build protofiles
 env.Append(CPPPATH="$TURBO_HOME")
 lib = env.StaticLibrary('turbo-rpc', [proto_files])
+Depends(lib,ret) # the library depends on having protoc headers installed
 ret = ret + env.Install("$TURBO_HOME/lib/", lib)