A couple errors dealing with uninitialized submodules

[Aaron Schrab <aaron@schrab.com>]

I was working with a fresh clone of a repository where I'd forgotten 
that one of the directories was setup as a submodule, so I hadn't 
initialized it.

I tried to add a symlink to a location outside the repository and this 
failed with an assertion (exact text in comment below). When looking 
into that I realized that the directory was meant to be a submodule and 
decided to try to change that.  So I tried to remove the submodule, and 
got an error (misleadingly) saying that couldn't be done because it uses 
a .git directory.

I first noticed this with git 2.9.3 from Debian unstable, but I also see 
it building from v2.10.1-502-g6598894 fetched from master recently.

The following script replicates both of these issues. These could both 
be classified as "don't do that", although at lease the assertion is 
quite ugly.

--- >8 ----
#!/bin/sh -e

directory=$(mktemp -d)
echo "Using directory '$directory'"
cd $directory
git init --quiet orig
(
  cd orig
  # Using a random, small repository for the submodule.
  git submodule --quiet add https://github.com/diepm/vim-rest-console.git sub
  git commit -m init >/dev/null
)
git clone --quiet orig dup
cd dup

(
  cd sub
  ln -s /tmp/dont_care
  # Next command aborts with
  # git: pathspec.c:317: prefix_pathspec: Assertion `item->nowildcard_len <= item->len && item->prefix <= item->len' failed.`
  git add . || : expected to fail
)

rm -f .git/index.lock
# Next command fails with error wrongly saying that the submodule uses a .git
# directory.  I believe that the real problem is that the uninitialized
# submodule has content.
git rm sub