imagine two users using the cgi interface:

* user A starts to edit an issue
* user B starts to edit an issue
* user A commits his changes
* user B commits his changes

when B commits, the changes A had committed
will be reverted. This problem could be solved
by adding a hidden field in the form that identifies
the version of the issue this change is relative to.
Then, on commit, the diffs could be computed and
be applied to the current version, i.e. merging the
change in, instead of copying it over.