Fix exception caught when mtime_map parent dir does not exist

This fixes an exception that was introduced in 342a6ae. Also, using
os.error does not catch IOError execeptions, so this has been changed as
well.
os.error does not catch IOError

Modified exceptions to include IOError
PEP8 (two lines between functions)
Merge pull request #6974 from terminalmage/fileserver-fix

Fix exception caught when mtime_map parent dir does not exist