Fix the way system files are handled at surf startup.

Fix the way system files are handled at surf startup.

1. Do not chmod existing directories.
2. Fix the handling of tilde expansion in paths, don't expand ~foo to
   $HOME/foo but to foo's home directory.
3. Separate the creation of files and directories. We don't have to
   worry anymore about pathnames having to end with a '/' to be correctly
   handled.

Signed-off-by: Christoph Lohmann <20h@r-36.net>