Merge branch 'jt/clone-recursesub-ref-advise'

The interaction between "git clone --recurse-submodules" and
alternate object store was ill-designed.  The documentation and
code have been taught to make more clear recommendations when the
users see failures.

* jt/clone-recursesub-ref-advise:
  submodule--helper: advise on fatal alternate error
  Doc: explain submodule.alternateErrorStrategy

Documentation/config/advice.txt

@@ -107,4 +107,7 @@ advice.*::
 		editor input from the user.
 	nestedTag::
 		Advice shown if a user attempts to recursively tag a tag object.
+	submoduleAlternateErrorStrategyDie:
+		Advice shown when a submodule.alternateErrorStrategy option
+		configured to "die" causes a fatal error.
 --

Documentation/config/submodule.txt

@@ -79,4 +79,6 @@ submodule.alternateLocation::
 submodule.alternateErrorStrategy::
 	Specifies how to treat errors with the alternates for a submodule
 	as computed via `submodule.alternateLocation`. Possible values are
-	`ignore`, `info`, `die`. Default is `die`.
+	`ignore`, `info`, `die`. Default is `die`. Note that if set to `ignore`
+	or `info`, and if there is an error with the computed alternate, the
+	clone proceeds as if no alternate was specified.