tests: add a new test for testing changing or clearing topics test-topic.t is getting bigger and bigger. This patch introduces a new test which includes test for clearing and changing topics. Since the tests are moved to a new file, this patch, removes those tests from test-topic.t also.

. $TESTDIR/testlib/pythonpath.sh

mkcommit() {
   echo "$1" > "$1"
   hg add "$1"
   hg ci -m "$1"
}

getid() {
   hg log --hidden --template '{node}\n' --rev "$1"
}

cat >> $HGRCPATH <<EOF
[alias]
debugobsolete=debugobsolete -d '0 0'
EOF