Merge branch 'nd/ignore-then-not-ignore'

Allow a later "!/abc/def" to override an earlier "/abc" that
appears in the same .gitignore file to make it easier to express
"everything in /abc directory is ignored, except for ...".

* nd/ignore-then-not-ignore:
dir.c: don't exclude whole dir prematurely if neg pattern may match
dir.c: make last_exclude_matching_from_list() run til the end

diff --cc Documentation/gitignore.txt
Simple merge

diff --cc dir.c
Simple merge

diff --cc t/t3001-ls-files-others-exclude.sh
Simple merge