Overwriting instead of appending to the file removes the [defaults]
section put into the file by run-tests.py.
It also defeats the --inotify option to run-tests.py.
(Nothing was broken yet, but the lack of -d "0 0" cause changeset
hashes to change unexpectedly in a test case I was editing.)
The two tests that used filtercr.py already used a slightly different
version, which explains why test-convert-svn-move.t changed after
switching to using $TESTDIR/filtercr.py.
Previously, we'd reset the entire progress bar state when a topic was
completed, even if it wasn't the outermost progress topic. Now we
print the state of the next progress topic on the stack if one is left
rather than reset the progress bar.
