Update featuring options to specifiy recording length, files to save, PGPLOT window, etc.
The usage is displayed by typing:

 polaris_start -h

	modified:   cuda_fft_xspec.cu
	modified:   polaris_start.c
	modified:   shm_alloc.c
	modified:   shm_k5data.inc
	modified:   shm_spec_view.c