test-histedit: fix instability creation test

The current test does not rewrite anything and therefor does not create any
instability.

We also clean up the repo state after the test. This required the rebase
extension.

tests/test-histedit-obsolete.t

@@ -14,6 +14,7 b' Enable obsolete'
   > publish=False
   > [extensions]'
   > histedit=
+  > rebase=
   > 
   > obs=${TESTTMP}/obs.py
   > EOF
@@ -148,8 +149,25 b' Test that rewriting leaving instability '
 
   $ hg up '.^'
   0 files updated, 0 files merged, 1 files removed, 0 files unresolved
-  $ hg phase --force --draft .
+  $ hg ph --force --draft '.'
   $ hg log -r 'children(.)'
   9:c13eb81022ca f (no-eol)
-  $ hg histedit -r '.'
+  $ cat > commands.txt <<EOF
+  > edit b346ab9a313d 6 c
+  > EOF
+  $ hg histedit -r '.' --commands commands.txt
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  adding c
+  abort: Make changes as needed, you may commit or record as needed now.
+  When you are finished, run hg histedit --continue to resume.
+  [255]
+  $ echo c >> c
+  $ hg histedit --continue
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+  $ hg log -r 'unstable()'
+  9:c13eb81022ca f (no-eol)
+
+stabilise
+
+  $ hg rebase  -r 'unstable()' -d .