Use Child Site Lost Password URL instead of Parent Lost Password URL

Filter the Lost Password URL and change the default behavior of
wp_lostpassword_url() so that it uses site_url() instead of
network_site_url(), but only if the current $_SERVER['REQUEST_URI']
differs from the Parent Site URL, as returned by network_site_url().
In a non-multisite environment, the default WordPress behavior (as of
v3.9.1) is used.

Also adds a new s2Member filter: ws_plugin__s2member_lost_password_url

See websharks/s2member#138
Merge branch '000000-dev' into feature/138

Conflicts:
	s2member/includes/hooks.inc.php - Fixed manually by updating with latest code and adding my changed line
Improve code quality and add filter for disabling Lost Password tweak.

See websharks/s2member#138
Limit tweak to the /wp-login.php system.

See websharks/s2member#138
Use urlencode_deep($args) when returning a tweaked Lost Password URL.

See websharks/s2member#138
Merge pull request #187 from websharks/feature/138

Use Child Site Lost Password URL instead of Parent Lost Password URL