Call to undefined function views_include() in views_attach.module on line 179

It's because Views module has default weight 10, this module have 0.

Please try this patch to views_attach.install file:

/**
 * Implementation of hook_install().
 */
function views_attach_install() {
   // Set the weight of booking_timeslots module to be one higher than calendars.
   $weight = (int) db_result(db_query("SELECT weight FROM {system} WHERE name = 'views'"));
   db_query("UPDATE {system} SET weight = %d WHERE name = 'views_attach'", $weight + 1);
}