Membership auto recur intermittantly not gettin checked

The hidden renew my membership automatically box is not getting ticked in some circumstances.

If you are logged in & fill in a contribution page with 2 membership options that are both always recurring configured via a membership block then when you click them they generally 'work' - but if you then switch to the other the box is deselected & does not re-select.

The situation is a bit peculiar. Basically there is a wierd calculation of the membership renewal-ness which is a combo of the membership_block value & the membership_type value & could be 0, 1, 2 or 4. It used to be only 1,2, or 4 - but then another scenario was broken. 4 means 2 points for membership block being forced & 2 points for membership type being forced & should be treated in the javascript the same as 2 - which would mean that one or the other is forced.

Potentially it should be the case that you need to have 4 & 2 only sometimes should work - but the fact I'm even saying that points to the fact it needs to be rewritten!

However, there is no doubt that 4 should be forced recurring & that it is currently not - so I will restrict the patch to addressing that.