[PATCH 0/2] completion of 'git [-C <dir>] checkout'

Continuing from the previous 'git [-C <dir>] diff' series, these two
patches correct completion for 'git checkout [-C <dir>] path<TAB>',
but without falling back to untracked paths, as "checkout paths out
of the index" is by definition about paths that appear in the index.

 1/2: completion: no-op refactoring of checkout completion
 2/2: completion: complete tracked paths for "git checkout"

 contrib/completion/git-completion.bash | 86 ++++++++++++++------------
 t/t9902-completion.sh                  | 27 ++++++++
 2 files changed, 73 insertions(+), 40 deletions(-)