Fix mappings so they correctly query "IS_BRICK".

[donnaaboise]

• Several mappings are built on brick grids. For example, the torus, annulus and latlong mappings can all include a brick mapping. But the query "IS_BRICK" was returning false. A check was added to the brick query to see if mapping contains a brick. If the mapping (latlong, torus, annulus, etc) contains a underlying brick mapping, the query IS_BRICK now returns True. This suggests that one of the clawpack examples (outside of GeoClaw, which doesn't use any clawpack mappings), should include a gauge test in the regression testing.
• Minor change to fclaw_gauges.c. Use fclaw_opt to get (mi,mj) when locating gauges, not brick mapping.