CRM-13831 - Add radio buttons to membership block for quickConfig pricesets

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* CRM-13831: Radio buttons do not appear in membership block for quickConfig pricesets
  http://issues.civicrm.org/jira/browse/CRM-13831
CRM-13831 - Fixed validation problems and incorrect amount calculations
by translating the membership type ID stored in selectMembership to
the price field option ID, stored in price_$id, as expected by all the
validation code as well as CRM_Price_BAO_PriceSet::processAmount.

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* CRM-13831: Radio buttons do not appear in membership block for quickConfig pricesets
  http://issues.civicrm.org/jira/browse/CRM-13831
Initialized uninitialized variable.