data-parser: A hard delimiter at end of line is not an empty field.

data-parser: A hard delimiter at end of line is not an empty field.

Until now, DATA LIST FREE(',') treated input like this:

    1,2,
    3,4,

as describing six fields, two of which were blank at the end of a line.
A bug report and subsequent experiments showed that in fact this is only
four fields, none of which is blank.  This commit fixes the problem and
adds a new test that should avoid regression against this issue.

Reported by Samuel Afflerbach.