Subnav link when viewing a private message incorrect

[DJPaul]

When viewing a private message, e.g. ​http://example.com/members/admin/messages/view/20/, a new item is added to the subnav which takes the format of "From: (last respondent)" which acts as a permalink to the current message.

The text of that subnav item is not in bold; it should be, to show the user which page they are on. The problem is that the subnav item is added late in messages_action_view_message(), with a slug of "view/ID." The bp_get_options_nav() function marks the current page's subnav item as bold, it does this by comparing the slug ("view/ID") with $bp->current_action ("view"). These are different so nothing is bolded.

If the slug argument to bp_core_new_subnav_item() in messages_action_view_message() is changed to "view", the bold is applied fine but then the link to the item is wrong; it takes you back to /members/admin/messages/view/. This causes a redirect back to the inbox.

[djpaul]

(In [4240]) Fix subnav link and highlighting when viewing a private message. Fixes #3169