Tale the code form one of the two libs and make your own lib from it just as if you where writing a lib of your own (example in playground) then change all vector_7 to something else like Vector_7!
Its a good general point that you need to check that libA is compatible with libB you also need to check that a lib is compatible with any shields you are using, for example the Servo code (from the playground) uses the same pinsas the motor shields.
Mark