Add require statements, revise lat/long extents code
Add require statements, revise lat/long extents code

Added require statements for the sp, raster, and
rgdal packages. Revised code to determine the plotting
extents (based on the met modelling domain) from the
lat/long coordinates written to the
'define.calmet.domain.out' file (in the working
directory).

rich-iannone/PuffR