Views+PCP: the URL field (to the PCP page) does not work

To reproduce: create a View with PCP pages. Add the fields ID and "CiviCRM Personal Campaign Pages: URL".

The second field will cause a http 500 error, since the field tries to call CRM_Utils_System::url() directly, but the "require" was not done, so it cannot find the function.

My patch is really simple: as for the CRM_Utils_System::href, which has a wrapper function called civicrm_views_href(), I created a wrapper called civicrm_views_url().

Note: I tested on a 4.0.x install, but I had backported the lastest 4.1 'views' code into it.