INT-3407: Fix TX-sync-processor potential NPE

JIRA: https://jira.spring.io/browse/INT-3407

Conflicts:

	spring-integration-core/src/main/java/org/springframework/integration/transaction/ExpressionEvaluatingTransactionSynchronizationProcessor.java
	spring-integration-core/src/test/java/org/springframework/integration/endpoint/PseudoTransactionalMessageSourceTests.java

Resolved.

	Fixed imports and reference to MessageBuilderFactory.