Some of the work here was done Tomasz Kolek.
When we click on "more conversations" in "Private Messages,"
we call it being "zoomed in." Before this change, when
new PMs arrived, we would rebuild the list and zoom out
again. Now we track the zoomed_in state with a variable.
Also, if you are zoomed in and switch from one PM narrow
to another, we also keep you zoomed in.
This fix also removes some extraneous/redundant code.
Fixes: #2561
Like the Stream Subject lists, Private messages are now shown
when the user clicks on the "Private message" link. User can drill in
to get more than 5 conversations. Selecting PMs from the user or group
PM lists on the right sidebar also opens the list & highlights the
selected conversation.
[Edited by tabbott@mit.edu to fix some small bugs.]
Aditya Bansal
Steve Howell
Umair Khan
Kara McNair