Introduce our own shutdown callback mechanism.

Instead of adding stuff to `_shutdown()`, we can now register a shutdown
routine from the respective `init()` function of our modules.

This also has the advantage, that we're sure they're called in reverse
order from how the initialization happened.

I didn't simply use `atexit()` because POSIX says that the number of
possible callbacks is limited (min 32) and I was not sure whether
we will maybe extend this number at one point.

Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>

tests/unittests/chatlog/stub_chatlog.c

@@ -27,7 +27,7 @@
 #include <xmpp/xmpp.h>
 
 void
-chat_log_init(void)
+chatlog_init(void)
 {
 }
 
@@ -65,11 +65,6 @@ chat_log_omemo_msg_in(ProfMessage* message)
 {
 }
 
-void
-chat_log_close(void)
-{
-}
-
 void
 groupchat_log_init(void)
 {

tests/unittests/config/stub_accounts.c

@@ -10,10 +10,6 @@ void
 accounts_load(void)
 {
 }
-void
-accounts_close(void)
-{
-}
 
 char*
 accounts_find_all(const char* const prefix, gboolean previous, void* context)

tests/unittests/log/stub_log.c

@@ -78,10 +78,6 @@ log_stderr_init(log_level_t level)
 {
 }
 void
-log_stderr_close(void)
-{
-}
-void
 log_stderr_handler(void)
 {
 }

tests/unittests/omemo/stub_omemo.c

@@ -7,10 +7,6 @@ void
 omemo_init(void)
 {
 }
-void
-omemo_close(void)
-{
-}
 
 char*
 omemo_fingerprint_autocomplete(const char* const search_str, gboolean previous)

tests/unittests/otr/stub_otr.c

@@ -33,10 +33,6 @@ void
 otr_init(void)
 {
 }
-void
-otr_shutdown(void)
-{
-}
 
 char*
 otr_libotr_version(void)

tests/unittests/pgp/stub_gpg.c

@@ -6,10 +6,6 @@ void
 p_gpg_init(void)
 {
 }
-void
-p_gpg_close(void)
-{
-}
 
 GHashTable*
 p_gpg_list_keys(void)

tests/unittests/test_server_events.c

@@ -17,6 +17,9 @@
 #include "plugins/plugins.h"
 #include "ui/window_list.h"
 
+
+void prof_shutdown(void);
+
 void
 console_shows_online_presence_when_set_online(void** state)
 {
@@ -35,7 +38,7 @@ console_shows_online_presence_when_set_online(void** state)
     sv_ev_contact_online(barejid, resource, NULL, NULL);
 
     roster_destroy();
-    plugins_shutdown();
+    prof_shutdown();
 }
 
 void
@@ -56,7 +59,7 @@ console_shows_online_presence_when_set_all(void** state)
     sv_ev_contact_online(barejid, resource, NULL, NULL);
 
     roster_destroy();
-    plugins_shutdown();
+    prof_shutdown();
 }
 
 void
@@ -77,7 +80,7 @@ console_shows_dnd_presence_when_set_all(void** state)
     sv_ev_contact_online(barejid, resource, NULL, NULL);
 
     roster_destroy();
-    plugins_shutdown();
+    prof_shutdown();
 }
 
 void
@@ -103,7 +106,7 @@ handle_offline_removes_chat_session(void** state)
 
     roster_destroy();
     chat_sessions_clear();
-    plugins_shutdown();
+    prof_shutdown();
 }
 
 void

tests/unittests/ui/stub_ui.c

@@ -63,10 +63,6 @@ ui_update(void)
 {
 }
 void
-ui_close(void)
-{
-}
-void
 ui_redraw(void)
 {
 }

tests/unittests/xmpp/stub_xmpp.c

@@ -47,10 +47,6 @@ session_disconnect(void)
 {
 }
 void
-session_shutdown(void)
-{
-}
-void
 session_process_events(void)
 {
 }
@@ -477,11 +473,6 @@ caps_lookup(const char* const jid)
     return NULL;
 }
 
-void
-caps_close(void)
-{
-}
-
 void
 caps_destroy(EntityCapabilities* caps)
 {