Bug fixes and enhancements

A2 and CRU SimCastMeta scripts now check to see whether resistant or
susceptible cultivar data were used and name output raster files
accordingly.

Extract_Risk_by_Country.R now includes the change in blight units.

Get_A2_Data.R now downloads proper precipitation file and unzips it.

Clean-up of NA flags in writeRaster() functions since using INT2S.