patch 7.4.1315

Problem:    Using a channel handle does not allow for freeing it when unused.
Solution:   Add the Channel variable type.

src/misc2.c

@@ -1138,6 +1138,9 @@ free_all_mem(void)
 # endif
 # ifdef FEAT_DIFF
     diff_clear(curtab);
+# endif
+# ifdef FEAT_CHANNEL
+    channel_free_all();
 # endif
     clear_sb_text();	      /* free any scrollback text */