Changes in .m files since last version:

* Modified makexbeachinput.m to write out wetz, which will tell us when a grid cell is wet and dry.
  This helps with post-processing codes.

* Modified xbeach2nc.m to read in wetz data and reshape and fixed data.u and v (it was saving data.utemp
  and data.vtemp).  Modified ncwrite_xbeach.m and nccreate_xbeach.m to include wetz data in the netcdf
  file.