Refactor all uses of like_escape() to use bp_esc_like()

WordPress 4.0 will deprecate like_escape(), due to a history of inconsistent
documentation and usage. Its replacement is a new method, $wpdb->esc_like(),
which will be available only in WP 4.0. For this reason, and because the
return value of $wpdb->esc_like() will not always be identical to that of
like_escape(), BP cannot do a straight swap of the old function for the new
one. Instead, we introduce a wrapper function that uses the core method if
available, and otherwise reproduces the logic of that method (for earlier
versions of WordPress).

Fixes #5701
slightly different syntax in some cases

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8541 cdf35c40-ae34-48e0-9cc9-0c9da1808c22