Merge branch 'cy/zsh-completion-SP-in-path'

With zsh, "git cmd path<TAB>" was completed to "git cmd path name"
when the completed path has a special character like SP in it,
without any attempt to keep "path name" a single filename.  This
has been fixed to complete it to "git cmd path\ name" just like
Bash completion does.

* cy/zsh-completion-SP-in-path:
completion: treat results of git ls-tree as file paths
zsh: complete unquoted paths with spaces correctly

diff --cc contrib/completion/git-completion.bash
Simple merge

diff --cc t/t9902-completion.sh
Simple merge