Chopping check for duplicates fix & filename cleanup

*Rather than load from file and filter for duplicates on each chop,
program now:

-checks if subpop ID directory/list has been loaded in memory, passes
stored value to chopper if in memory
-if not in memory, loads source file & filters for duplicates, stores
in memory

So each file is only read & checked for duplicates once then loaded
from memory from thereout, should reduce disk access & search
bottlenecks

*Chopfiles now marked as "d0i1v" for day 0 of chop, 1st intervention
scripted, of type vaccine. May prevent errors for long chops. Also,
.txt suffix moved to end of filename if present.
tweak