Handle fetching/pushing symlinks instead of creating empty files

Handle fetching/pushing symlinks instead of creating empty files

This makes symlinks in proj/init work, and should also fix the use of
symlinks in other place. Also, the code should now detect other
non-regular files being fetched and return an error message in this case.

Fixes bz#141

Signed-off-by: Tobias Ulmer <tu@emlix.com>