table-casereader: Put space between columns.

When table_casereaders are pasted together next to each other, there
should normally be a little bit of space between neighboring columns,
instead of having them directly abutting.  This makes the output of
LIST, for example, much more readable.

Without this commit, LIST output for three variables named x, y, and
z, all with F1.0 format, looks something like this:

xyz
---
111
222
311
412
521
612
711
811
912

With this commit, it looks like this:

x y z
-----
1 1 1
2 2 2
3 1 1
4 1 2
5 2 1
6 1 2
7 1 1
8 1 1
9 1 2