git add: rework the logic to warn "git add <pathspec>..." default change

The earlier logic to warn against "git add subdir" that is run
without "-A" or "--no-all" was only to check any <pathspec> given
exactly spells a directory name that (still) exists on the
filesystem.  This had number of problems:

 * "git add '*dir'" (note that the wildcard is hidden from the
   shell) would not trigger the warning.

 * "git add '*.py'" would behave differently between the current
   version of Git and Git 2.0 for the same reason as "subdir", but
   would not trigger the warning.

 * "git add dir" for a submodule "dir" would just update the index
   entry for the submodule "dir" without ever recursing into it, and
   use of "-A" or "--no-all" would matter.  But the logic only
   checks the directory-ness of "dir" and gives an unnecessary
   warning.

Rework the logic to detect the case where the behaviour will be
different in Git 2.0, and issue a warning only when it matters.
Even with the code before this warning, "git add subdir" will have
to traverse the directory in order to find _new_ files the index
does not know about _anyway_, so we can do this check without adding
an extra pass to find if <pathspec> matches any removed file.

This essentially updates the "add_files_to_cache()" public API to
"update_files_in_cache()" API that is internal to "git add", because
with the "--all" option, the function is no longer about "adding"
paths to the cache, but is also used to remove them.

There are other callers of the former from "checkout" (used when
"checkout -m" prepares the temporary tree that represents the local
modifications to be merged) and "commit" ("commit --include" that
picks up local changes in addition to what is in the index).  Since
ADD_CACHE_IGNORE_ERRORS (aka "--no-all") is not used by either of
them, once dust settles after Git 2.0 and the warning becomes
unnecessary, we may want to unify these two functions again.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
line-log: fix documentation formatting

The second paragraph of the added description for the -L option
"<start> and <end> can take one of these forms:", and the list of
forms that follow the headline, were indented one level too short,
due to the missing "+" to signal that the next paragraph continues
the previous one.

Also "You can specify this option more than once" is about the -L
option, not about its various forms of starting and ending points.
Move it to the end of the main text.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
git add: rephrase the "removal will cease to be ignored" warning

Now the logic to decide when to warn has been tightened, we know the
user is in a situation where the current and future behaviours will
be different.  Spell out what happens with these two versions and
how to explicitly ask for the behaviour, and suggest "git status" as
a way to inspect the current status.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'jc/add-2.0-delete-default' (early part) into next

Tighten the logic to decide when to warn so that we warn only when
the difference between the current and the future behaviours matter,
and tweak the wording of the warning message.

* 'jc/add-2.0-delete-default' (early part):
  git add: rephrase the "removal will cease to be ignored" warning
  git add: rework the logic to warn "git add <pathspec>..." default change
Merge branch 'tr/line-log' into next

* tr/line-log:
  line-log: fix documentation formatting