feat(caps): add cache clearing to /caps

Add /caps clear to wipe the local capabilities cache.
Implement autocomplete for new subcommand.

src/command/cmd_funcs.c

@@ -70,6 +70,7 @@
 #include "xmpp/stanza.h"
 #include "xmpp/vcard_funcs.h"
 #include "xmpp/xmpp.h"
+#include "xmpp/capabilities.h"
 
 #ifdef HAVE_LIBOTR
 #include "otr/otr.h"
@@ -3387,6 +3388,12 @@ cmd_caps(ProfWin* window, const char* const command, gchar** args)
         return TRUE;
     }
 
+    if (g_strcmp0(args[0], "clear") == 0) {
+        caps_cache_clear();
+        cons_show("Capabilities cache cleared.");
+        return TRUE;
+    }
+
     switch (window->type) {
     case WIN_MUC:
         if (args[0]) {
@@ -3405,6 +3412,7 @@ cmd_caps(ProfWin* window, const char* const command, gchar** args)
         break;
     case WIN_CHAT:
     case WIN_CONSOLE:
+    case WIN_XML:
         if (args[0]) {
             auto_jid Jid* jid = jid_create(args[0]);