fixed nasty data loss bug

I wanted to try to guard against it in Command.Add too, but it's a case of
garbage in, garbage out. Once Command.Add has been told it's dealing with a
dummy symlink, it goes and deletes it, and even though the object it
thinks it points to is not present in the annex, it's Command.Add is still
doing the right thing to go ahead and add the broken symlink. So the two
fixes I was able to put in will have to do.

debian/changelog

@@ -25,6 +25,9 @@ git-annex (4.20130710) UNRELEASED; urgency=low
   * webapp: Differentiate between creating a new S3/Glacier/WebDav remote,
     and initializing an existing remote. When creating a new remote, avoid
     conflicts with other existing (or deleted) remotes with the same name.
+  * Bug fix: Adding files that contained a tarball of a git-annex repository,
+    or other content in the first line that looks like a git-annex link,
+    could cause git-annex add to malfunction and lose the file content.
 
  -- Joey Hess <joeyh@debian.org>  Tue, 09 Jul 2013 19:17:13 -0400
 

doc/bugs/git_annex_add_removes_file_with_no_data_left.mdwn

@@ -94,3 +94,5 @@ lrwxrwxrwx 1 andrew andrew       195 Jul 12 02:20 Expressionlessm.tar -> ../.git
 
 # End of transcript or log.
 """]]
+
+> [[done]]; this bug is now prevented on several levels. --[[Joey]]