wrapper: clean the source dir before a checkout

Git doesn't clear folders containing untracked files when switching to
another branch. The autohelp script uses invalid .pyc files when such
switches happen in the diff_branches.py script. This change removes all
the .pyc files before a checkout to avoid this problem.

Change-Id: I0acd0308a3651b27d158546036de5cb0b42d974c

autogenerate_config_docs/autohelp-wrapper

@@ -154,6 +154,7 @@ if [ "$FAST" -eq 0 ] ; then
 
         (
             cd $SOURCESDIR/$project
+            find $project -name "*.pyc" -delete
             GIT_CMD="git show-ref --verify --quiet refs/heads/$BRANCH"
             if $GIT_CMD; then
                 git checkout $BRANCH