completion: treat results of git ls-tree as file paths

completion: treat results of git ls-tree as file paths

Let's say there are files named 'foo bar.txt', and 'abc def/test.txt' in
repository. When following commands trigger a completion:

    git show HEAD:fo<Tab>
    git show HEAD:ab<Tab>

The completion results in bash/zsh:

    git show HEAD:foo bar.txt
    git show HEAD:abc def/

Where the both of them have an unescaped space in paths, so they'll be
misread by git. All entries of git ls-tree either a filename or a
directory, so __gitcomp_file() is proper rather than __gitcomp_nl().

Note the commit f12785a3, which handles quoted paths properly. Like this
case, we should dequote $cur_ for ?*:* case. For example, let's say
there is untracked directory 'abc deg', then trigger a completion:

    git show HEAD:abc\ de<Tab>
    git show HEAD:'abc de<Tab>
    git show HEAD:"abc de<Tab>

should uniquely complete 'abc def', but bash completes 'abc def' and
'abc deg' instead. In zsh, triggering a completion:

    git show HEAD:abc\ def/<Tab>

should complete 'test.txt', but nothing comes. The both problems will be
resolved by dequoting paths.

__git_complete_revlist_file() passes arguments to __gitcomp_nl() where
the first one is a list something like:

    abc def/Z
    foo bar.txt Z

where Z is the mark of the EOL.

- The trailing space of blob in __git ls-tree | sed.
  It makes the completion results become:

      git show HEAD:foo\ bar.txt\ <CURSOR>

  So git will try to find a file named 'foo bar.txt ' instead.

- The trailing slash of tree in __git ls-tree | sed.
  It makes the completion results on zsh become:

      git show HEAD:abc\ def/ <CURSOR>

  So that the last space on command like should be removed on zsh to
  complete filenames under 'abc def/'.

Signed-off-by: Chayoung You <yousbe@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>