Add e_activity_get_last_known_text().

Evolution is still occasionally getting stuck on shutdown, and although
the evolution-shell log domain shows debug messages for activities that
are preventing shutdown, they frequently look like this:

(evolution:13534): evolution-shell-DEBUG: 5 active 'mail' activities:
(evolution:13534): evolution-shell-DEBUG: * (no description)
(evolution:13534): evolution-shell-DEBUG: * (no description)
(evolution:13534): evolution-shell-DEBUG: * (no description)
(evolution:13534): evolution-shell-DEBUG: * (no description)
(evolution:13534): evolution-shell-DEBUG: * (no description)

I think the lack of descriptions is from CamelOperations popping all
their pushed messages, which is correct behavior but doesn't help us
debug the problem.

e_activity_get_last_known_text() returns the most recent _non-empty_
text value set on the EActivity.  So our debug message can fall back
to that if the EActivity has no description at shutdown:

(evolution:13534): evolution-shell-DEBUG: * (was "blah, blah, blah")

1 files changed, 6 insertions, 0 deletions

diff --git a/shell/e-shell-backend.c b/shell/e-shell-backend.c
index 5f7666b238..e4926c5c0a 100644
--- a/shell/e-shell-backend.c
+++ b/shell/e-shell-backend.c
@@ -105,12 +105,18 @@ shell_backend_debug_list_activities (EShellBackend *shell_backend)
 	for (link = head; link != NULL; link = g_list_next (link)) {
 		EActivity *activity = E_ACTIVITY (link->data);
 		gchar *description;
+		const gchar *was;
 
 		description = e_activity_describe (activity);
+		was = e_activity_get_last_known_text (activity);
+
 		if (description != NULL)
 			g_debug ("* %s", description);
+		else if (was != NULL)
+			g_debug ("* (was \"%s\")", was);
 		else
 			g_debug ("* (no description)");
+
 		g_free (description);
 	}
 }