Rationale:
- csvformat -U2 doesn't work -- it's a bug.
- csvformat -U2 without -u2 means that we'll have to detect which columns are numeric, to convert the input (string) values to output (decimal) values.
- We don't want to change anything to the other columns.
- We need to keep things as quick as possible.
This is an attempt at solving this bug while responding to the above constraints. Feel free to comment or hack it!