fix doctests in sagenb/notebook/cell.py
fix doctests in sagenb/notebook/notebook.py
fix KeyError in user_manager.py
fix doctest in user_manager.py
fix doctests in sagenb/notebook/worksheet.py
add nodoctest.py to directories that should not be doctested
replace tmp_dir+'.sagenb' with tmp_dir(ext='.sagenb')
Merge pull request #161 from ppurka/doctests

Fix doctests in sagenb directory