Fix mark-message translation and keybind menu.

Move the OP_MARK_MESSAGE and hotkey macro from MENU_GENERIC to the
MENU_MAIN keymap. Putting the macro under generic prevents it from
overriding a keybinding in the index (even if the function is bound to
noop). Additionally, the macro can only be executed from the index,
so it doesn't make sense as a generic keybinding.

Use the term "hotkey" in both the OPS and km_bind description.

Mark the km_bind description translatable.

Add L10N messages for the new translation strings.

OPS

···
 OP_MAIN_TAG_PATTERN "tag messages matching a pattern"
 OP_MAIN_UNDELETE_PATTERN "undelete messages matching a pattern"
 OP_MAIN_UNTAG_PATTERN "untag messages matching a pattern"
-OP_MARK_MSG "create a hot-key macro for the current message"
+OP_MARK_MSG "create a hotkey macro for the current message"
 OP_MIDDLE_PAGE "move to the middle of the page"
 OP_NEXT_ENTRY "move to the next entry"
 OP_NEXT_LINE "scroll down one line"

curs_main.c

···
 	  char buf[128];
 
 	  buf[0] = '\0';
+          /* L10N: This is the prompt for <mark-message>.  Whatever they
+             enter will be prefixed by $mark_macro_prefix and will become
+             a macro hotkey to jump to the currently selected message. */
 	  if (!mutt_get_field (_("Enter macro stroke: "), buf, sizeof(buf),
 	  		       MUTT_CLEAR) && buf[0])
 	  {
 	    snprintf(str, sizeof(str), "%s%s", MarkMacroPrefix, buf);
 	    snprintf(macro, sizeof(macro),
 		     "<search>~i \"%s\"\n", CURHDR->env->message_id);
-	    km_bind(str, MENU_GENERIC, OP_MACRO, macro, "Message hotkey");
+            /* L10N: "message hotkey" is the key bindings menu description of a
+               macro created by <mark-message>. */
+	    km_bind(str, MENU_MAIN, OP_MACRO, macro, _("message hotkey"));
 
+            /* L10N: This is echoed after <mark-message> creates a new hotkey
+               macro.  %s is the hotkey string ($mark_macro_prefix followed
+               by whatever they typed at the prompt.) */
 	    snprintf(buf, sizeof(buf), _("Message bound to %s."), str);
 	    mutt_message(buf);
 	    dprint (1, (debugfile, "Mark: %s => %s\n", str, macro));
 	  }
 	}
 	else
+          /* L10N: This error is printed if <mark-message> cannot find a
+             Message-ID for the currently selected message in the index. */
 	  mutt_error _("No message ID to macro.");
 	break;
 

functions.h

···
   { "previous-line",	OP_PREV_LINE,		"<" },
   { "half-up",		OP_HALF_UP,		"[" },
   { "half-down", 	OP_HALF_DOWN,		"]" },
-  { "mark-message",	OP_MARK_MSG,		"~" },
   { "help",		OP_HELP,		"?" },
   { "tag-prefix",	OP_TAG_PREFIX,		";" },
   { "tag-prefix-cond",	OP_TAG_PREFIX_COND,	NULL },
···
   { "set-flag",			OP_MAIN_SET_FLAG,		"w" },
   { "clear-flag",		OP_MAIN_CLEAR_FLAG,		"W" },
   { "display-message",		OP_DISPLAY_MESSAGE,		MUTT_ENTER_S },
+  { "mark-message",		OP_MARK_MSG,			"~" },
   { "buffy-list",		OP_BUFFY_LIST,			"." },
   { "sync-mailbox",		OP_MAIN_SYNC_FOLDER,		"$" },
   { "display-address",		OP_DISPLAY_ADDRESS,		"@" },