JPSSnagg

nagg.h
    Add prototype for get_granule_pattern().
nagg_get_granules.c
    Add get_granule_pattern() function.
nagg_write_granules.c
    Add get_product_id_by_idx() function.
    Update code to write missing granules from granule_pattern instead
    of from previous granule.

Tests needed for missing granules.  Tested manually; will add test to make check tomorrow.

Tested jam & koala, icc & gcc.