cosmetic cleanup of all_perms(); no change in functionality

* restore function definition to original location in the file
* restore function documentation
* cleanup slicing into daysSliced and daysLast
* catenate tuples into new tuple instead of converting to list

Steve, in general if your are changing implementation but not changing
functionality (inputs + outputs) then leave in the same function in
the first place.  Don't fear losing the old code because it is all
in version control history.