Transaction manager cache fails to repopulate when multiple transaction managers defined

When TransactionAspectSupport is initialized, the transaction manager cache is populated by the setTransactionManager method. At this point there can be multiple TransactionInterceptor instances defined, each with its own cache, with no conflicts.

However, as soon as the transaction cache entry in TransactionAspectSupport is cleared by the garbage collector, the transaction manager bean is then looked up by type, which leads to a NoUniqueBeanDefinitionException if multiple transaction managers are defined in your application context.

This is a regression caused by SPR-14511.