Fix work directory cleanup : never go deeper than one subdirectory

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Merge branch 'testing' of github.com:jflesch/paperwork into testing
Merge branch 'testing' into unstable

Conflicts:
	src/paperwork/backend/docsearch.py

Signed-off-by: Jerome Flesch <jflesch@gmail.com>