Content fetching APIs - minor fixes

[roadscape]

1. In get_state "@user/posts", comment keys are returned in account.posts without '@author/' prefix, which is not consistent with how blogs and feeds are returned (as of late).

2. Loading of "recent replies" seems to be broken (after the 1st page). Here's the method: get_replies_by_last_update(start_parent_author, start_permlink, limit)

Locally, I got the method to work (seemingly) as expected by making the following change:

-   bool filter_by_parent_author = true;
+   bool filter_by_parent_author = false;

[theoreticalbts]

@mvandeberg if this is merged, can this ticket be closed?