Bug 593406 - Permissions set to 777 after copying via Nautilus

When doing a g_file_copy() with nofollow-symlinks (to copy a link for
example), the later copying of the file attributes copies the source
links 777 attributes to the target's attributes. As chmod affects the
symlink target, this would cause such copies to always set the target to
777 mode.

This patch makes setting the mode with nofollow-symlinks fail with
NOT_SUPPORTED.

The aforementioned g_file_copy() will still succeed, because it ignores
errors of the attribute copy.

This patch includes the whole patchset from master:
3826963e
bb7852e3
48e0af01
e695c093