Document ls-files -t as semi-obsolete.

The behavior of "git ls-files -t" is very misleading (see
http://thread.gmane.org/gmane.comp.version-control.git/126516 and
http://thread.gmane.org/gmane.comp.version-control.git/144394/focus=144397
for examples of mislead users) and badly documented, hence we point the
users to superior alternatives.

The feature is marked as "semi-obsolete" but not "scheduled for removal"
since it's a plumbing command, scripts might use it, and Git testsuite
already uses it to test the state of the index.
Signed-off-by: NMatthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-ls-files.txt

@@ -106,8 +106,16 @@ OPTIONS
 	with `-s` or `-u` options does not make any sense.
 
 -t::
-	Identify the file status with the following tags (followed by
-	a space) at the start of each line:
+	This feature is semi-deprecated. For scripting purpose,
+	linkgit:git-status[1] `--porcelain` and
+	linkgit:git-diff-files[1] `--name-status` are almost always
+	superior alternatives, and users should look at
+	linkgit:git-status[1] `--short` or linkgit:git-diff[1]
+	`--name-status` for more user-friendly alternatives.
++
+This option identifies the file status with the following tags (followed by
+a space) at the start of each line:
+
 	H::	cached
 	S::	skip-worktree
 	M::	unmerged