Fix 'Show the Toolbar for logged out users' setting.

bp_core_load_admin_bar() uses the show_admin_bar() function; this
function toggles the WP toolbar visibiility.

WP recommends to use show_admin_bar() on 'plugins_loaded':
https://codex.wordpress.org/Function_Reference/show_admin_bar#Notes

Therefore, this commit changes when bp_core_load_admin_bar() runs
from 'bp_init' to 'bp_loaded'.

Fixes #4771.
Change 'title' attribute for topic links in group forum loop template.

In the topic title link, bp_the_topic_title() is used twice: once
in the 'title' attribute and again for the anchor text.

For plugin devs wanting to manipulate the HTML markup for the topic
title, this would cause unintended output in the 'title' attribute.

Therefore, this commit removes bp_the_topic_title() from the 'title'
attribute for topic links.

Fixes #4770. Props chouf1.
Switch TEMPLATEPATH constant to get_template_directory() function.

Fixes #4744. Props fanquake.
POT, generated from r6726
Add a is_new_install $_GET parameter when redirecting to About on fresh install

When building the About/What's New Dashboard panel, it's helpful to know
whether this is a new BuddyPress install, or an upgrade from a previous
version.

See #4727
First pass at copy for About/What's New panel for 1.7.

See #4727
Pinking shears
POT, generated from r6730
Allow activity items to be deleted when the user_id key is empty

Some plugins create activity items that are not attached to a specific user_id.
The activity deletion request handlers (AJAX and bp-activity-actions) prevent
deletion of activity items when the item's user_id value is empty. This
changeset moves this security measure to the bp_activity_user_can_delete()
function, so that anonymous activity items can still be deleted by item admins.

Props magnus78

Fixes #4735
Pinking shears
Make BP respect the value of "use akismet for activity checks" preference. Fixes #4773

This bug was introduced during 1.6 development.
Fix typo on the xprofile admin screen. Fixes #4777, props slaFFik
POT, generated from r6735
Update new credits screen with current 1.7 props list and add a few missing textdomains to i18n functions. See #4727
POT, generated from r6737
Better friend ID handling in ajax add/remove friend handler in bp-default and bp-legacy. Props Maty.
Cast more POST values and code prettifying in bp-default and bp-legacy. Props Maty.
POT, generated from r6740
More regex fixes in bp_activity_thumbnail_content_images()

Fixes #4488
Documentation for regex in bp_activity_thumbnail_content_images()