reset: support "--mixed --intent-to-add" mode

When --mixed is used, entries could be removed from index if the
target ref does not have them. When "reset" is used in preparation for
commit spliting (in a dirty worktree), it could be hard to track what
files to be added back. The new option --intent-to-add simplifies it
by marking all removed files intent-to-add.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Merge branch 'nd/tag-doc'

* nd/tag-doc:
  git-tag.txt: <commit> for --contains is optional
Merge branch 'aj/ada-diff-word-pattern'

* aj/ada-diff-word-pattern:
  userdiff: update Ada patterns
Merge branch 'ow/manpages-typofix'

Various typofixes, all looked correct.

* ow/manpages-typofix:
  Documentation: fix typos in man pages
Git 1.9.0-rc3

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Sync with 1.9.0-rc3

* master:
  Git 1.9.0-rc3
Merge branch 'nd/reset-intent-to-add' into next

* nd/reset-intent-to-add:
  reset: support "--mixed --intent-to-add" mode