Merge branch 'kh/doc-committer-date-is-author-date'

The "--committer-date-is-author-date" option of "git am/rebase" is
a misguided one.  The documentation is updated to discourage its
use.

* kh/doc-committer-date-is-author-date:
  doc: warn against --committer-date-is-author-date

Author: gitster

Documentation/git-am.adoc

@@ -162,6 +162,13 @@ Valid <action> for the `--whitespace` option are:
 	commit creation as the committer date. This allows the
 	user to lie about the committer date by using the same
 	value as the author date.
++
+WARNING: The history walking machinery assumes that commits have
+non-decreasing commit timestamps. You should consider if you really need
+to use this option. Then you should only use this option to override the
+committer date when applying commits on top of a base which commit is
+older (in terms of the commit date) than the oldest patch you are
+applying.
 
 --ignore-date::
 	By default the command records the date from the e-mail

Documentation/git-rebase.adoc

@@ -474,6 +474,13 @@ See also INCOMPATIBLE OPTIONS below.
 	Instead of using the current time as the committer date, use
 	the author date of the commit being rebased as the committer
 	date. This option implies `--force-rebase`.
++
+WARNING: The history walking machinery assumes that commits have
+non-decreasing commit timestamps. You should consider if you really need
+to use this option. Then you should only use this option to override the
+committer date when rebasing commits on top of a base which commit is
+older (in terms of the commit date) than the oldest commit you are
+applying (in terms of the author date).
 
 --ignore-date::
 --reset-author-date::