bug#13949: 24.4.1; `fill-paragraph' should not always put the buffer as modified

[Jaakov]

For every hash function X, there is a set m(X) of people who are likely 
to abhor hash-checked-implementation of buffer modification:

m(X)  =  the maintainers of databases of collisions for X.

For each X: today, m(X) may be empty, small, or large, but, as the time 
goes by and hash functions remain, m(X) will be growing.