doc: be more precise on (fetch|push).recurseSubmodules

The default value also depends on the value of submodule.recurse.
Use this opportunity to correct some grammar mistakes in
Documentation/config/fetch.txt signaled by Robert P. J. Day.

Also mention `fetch.recurseSubmodules` in fetch-options.txt. In
git-push.txt, `push.recurseSubmodules` is implicitly mentioned (by
explaining how to disable it), so no need to add it there.

Lastly add a link to `git-fetch` in `git-pull.txt` to explain the
meaning of `--recurse-submodules` there.

Signed-off-by: Damien Robert <damien.olivier.robert+git@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/fetch.txt

@@ -1,11 +1,14 @@
 fetch.recurseSubmodules::
-	This option can be either set to a boolean value or to 'on-demand'.
+	This option controls whether `git fetch` (and the underlying fetch
+	in `git pull`) will recursively fetch into populated submodules.
+	This option can be set either to a boolean value or to 'on-demand'.
 	Setting it to a boolean changes the behavior of fetch and pull to
-	unconditionally recurse into submodules when set to true or to not
-	recurse at all when set to false. When set to 'on-demand' (the default
-	value), fetch and pull will only recurse into a populated submodule
-	when its superproject retrieves a commit that updates the submodule's
+	recurse unconditionally into submodules when set to true or to not
+	recurse at all when set to false. When set to 'on-demand', fetch and
+	pull will only recurse into a populated submodule when its
+	superproject retrieves a commit that updates the submodule's
 	reference.
+	Defaults to 'on-demand', or to the value of 'submodule.recurse' if set.
 
 fetch.fsckObjects::
 	If it is set to true, git-fetch-pack will check all fetched

Documentation/config/push.txt

@@ -112,3 +112,5 @@ push.recurseSubmodules::
 	is 'no' then default behavior of ignoring submodules when pushing
 	is retained. You may override this configuration at time of push by
 	specifying '--recurse-submodules=check|on-demand|no'.
+	If not set, 'no' is used by default, unless 'submodule.recurse' is
+	set (in which case a 'true' value means 'on-demand').

Documentation/fetch-options.txt

@@ -163,7 +163,8 @@ ifndef::git-pull[]
 	value. Use 'on-demand' to only recurse into a populated submodule
 	when the superproject retrieves a commit that updates the submodule's
 	reference to a commit that isn't already in the local submodule
-	clone.
+	clone. By default, 'on-demand' is used, unless
+	`fetch.recurseSubmodules` is set (see linkgit:git-config[1]).
 endif::git-pull[]
 
 -j::

Documentation/git-pull.txt

@@ -86,8 +86,7 @@ OPTIONS
 
 --[no-]recurse-submodules[=yes|on-demand|no]::
 	This option controls if new commits of all populated submodules should
-	be fetched and updated, too (see linkgit:git-config[1] and
-	linkgit:gitmodules[5]).
+	be fetched and updated, too (see linkgit:git-fetch[1], linkgit:git-config[1] and linkgit:gitmodules[5]).
 +
 If the checkout is done via rebase, local submodule commits are rebased as well.
 +