Fix AJAX pagination when clicked page number is 1000 or more.

Previously, BP's javascript was converting the paginated element
content to a number with the Number() function.  This doesn't work
with comma-seperated number strings (eg. 1,000), which returned a NaN
value causing problems during the AJAX callback.

This commit changes the way the page number is parsed in BP's
javascript by grabbing the page number from the 'href' attribute.
Thereby, ensuring that AJAX pagination works for pages greater than
1000.

Fixes #5404

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7946 cdf35c40-ae34-48e0-9cc9-0c9da1808c22