added Makefile so rosmake works
fixed compile error:

  /home/forrest/ros/pgr_camera/src/libpgrcam/pgr_camera.cpp: In member function ‘void pgr_camera::Camera::start()’:
  /home/forrest/ros/pgr_camera/src/libpgrcam/pgr_camera.cpp:200:59: error: invalid conversion from ‘void (*)(FlyCapture2::Image*, void*)’ to ‘FlyCapture2::ImageEventCallback {aka void (*)(FlyCapture2::Image*, const void*)}’ [-fpermissive]
  /usr/include/flycapture/Camera.h:234:23: error:   initializing argument 1 of ‘virtual FlyCapture2::Error FlyCapture2::Camera::StartCapture(FlyCapture2::ImageEventCallback, const void*)’ [-fpermissive]
fixed linker not linking flycapture library for some reason