Contribution Page Membership Block Should Exclude Disabled Membership Types

Currently, if you've selected a Membershp Type to be included in a Contribution Page Membership Signup block - and THEN you disable that membership type (Administer >> Membership Types) - the membership type is still included then the online contribution page is rendered (because it is still included in the civicrm_membership_block.membership_types list).

Add a check for membership_type.is_active to the code which builds the membership_type radio button elements in the contribution pages' membership block.