added datastack test data. see #3793.

data_stack/carbon_pools_samp.csv

data_stack/dem/dblbnd.adf

data_stack/dem/hdr.adf

data_stack/dem/log

data_stack/dem/metadata.xml

data_stack/dem/prj.adf

data_stack/dem/sta.adf

data_stack/dem/vat.adf

data_stack/dem/w001001.adf

data_stack/dem/w001001x.adf

data_stack/landcover.tif

data_stack/watersheds.dbf

data_stack/watersheds.prj

data_stack/watersheds.sbn

data_stack/watersheds.sbx

data_stack/watersheds.shp

data_stack/watersheds.shp.xml

data_stack/watersheds.shx