push: parse and set flag for "--force-if-includes"

The previous commit added the necessary machinery to implement the
"--force-if-includes" protection, when "--force-with-lease" is used
without giving exact object the remote still ought to have. Surface
the feature by adding a command line option and a configuration
variable to enable it.

 - Add a flag: "TRANSPORT_PUSH_FORCE_IF_INCLUDES" to indicate that the
   new option was passed from the command line of via configuration
   settings; update command line and configuration parsers to set the
   new flag accordingly.

 - Introduce a new configuration option "push.useForceIfIncludes", which
   is equivalent to setting "--force-if-includes" in the command line.

 - Update "remote-curl" to recognize and pass this option to "send-pack"
   when enabled.

 - Update "advise" to catch the reject reason "REJECT_REF_NEEDS_UPDATE",
   set when the ref status is "REF_STATUS_REJECT_REMOTE_UPDATED" and
   (optionally) print a help message when the push fails.

 - The new option is a "no-op" in the following scenarios:
    * When used without "--force-with-lease".
    * When used with "--force-with-lease", and if the expected commit
      on the remote side is specified as an argument.

Signed-off-by: Srinidhi Kaushik <shrinidhi.kaushik@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/advice.h b/advice.h
index 16f2c11..bc24329 100644
--- a/advice.h
+++ b/advice.h
@@ -11,6 +11,7 @@ extern int advice_push_already_exists;
 extern int advice_push_fetch_first;
 extern int advice_push_needs_force;
 extern int advice_push_unqualified_ref_name;
+extern int advice_push_ref_needs_update;
 extern int advice_status_hints;
 extern int advice_status_u_option;
 extern int advice_status_ahead_behind_warning;
@@ -60,6 +61,7 @@ extern int advice_add_empty_pathspec;
 	ADVICE_PUSH_UNQUALIFIED_REF_NAME,
 	ADVICE_PUSH_UPDATE_REJECTED_ALIAS,
 	ADVICE_PUSH_UPDATE_REJECTED,
+	ADVICE_PUSH_REF_NEEDS_UPDATE,
 	ADVICE_RESET_QUIET_WARNING,
 	ADVICE_RESOLVE_CONFLICT,
 	ADVICE_RM_HINTS,