Improved plural i18n for pagination links

Cases where there is only one page of results will now read, eg, "...of 1
member" instead of "...of 1 members".

Where the pagination links are put through apply_filters(), this changeset
also adds the passing of the $from_num, $to_num, and $total values to the
filter.

Fixes #5107

Props imath

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7439 cdf35c40-ae34-48e0-9cc9-0c9da1808c22