Do not let lstree output recursively when a directory whose name is a prefix of the others is given in the path list.

Here is how to reproduce the bug:

git init
mkdir prefix && touch prefix/a && git add prefix/a
mkdir prefixdir && touch prefixdir/b && git add prefixdir/b
git commit -a -m "If -r is not given, ls-tree should not show files in subdirs."
git ls-tree --name-only HEAD prefix  # works as expected
git ls-tree --name-only HEAD prefixdir  # works as expected
git ls-tree --name-only HEAD prefix prefixdir  # shows file, not dir

The output of the last command is 

prefix/a
prefixdir

But it should be

prefix
prefixdir

The patch fixes the problem.