Warn if link can't be created

Check if the link source already exists and that it is not a link.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Warn if link exists with wrong target

Check if the symbolic link already exists and warn if it targets
something other than what it is supposed to.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>