Throw a proper exception if no convert is found

Prior to this commit, no exception was raised if a message could not
be converted to the requested payload because no suitable converter
were found.

This commit adds an explicit check if the converted payload is null.

Issue: SPR-11817
Upgrade Eclipse project settings for Java 8

 - Set the eclipse.jdt source and target compatibility to 1.8 in
   ide.gradle.

 - Updated the instructions in import-into-eclipse.sh to reflect minimum
   requirements for building Spring Framework 4.1 against Java 8 with
   Eclipse and STS

Issue: SPR-11831
Upgrade spring-test tests to Hibernate 4

This commit upgrades Hibernate-based integration tests in the
spring-test module to use Hibernate 4 instead of 3 and Hibernate
Validator 5 instead of 4. This streamlines and simplifies our
dependency management at the same time.

Issue: SPR-11834
Eclipse project deps come after third-party libs

Prior to this commit, the ordering of classpath entries in the
generated Eclipse .classpath files did not align with the intended
dependency management configured in the Gradle build. Specifically,
project dependencies often came before dependencies on third-party
libraries required for the given project, causing the project not to
compile in Eclipse.

This commit fixes this issue by introducing new functionality in the
ide.gradle script that moves all project dependencies to the end of the
generated classpath.

Issue: SPR-11836
Introduce annotation to execute SQL scripts in the TCF

Work In Progress: functionally complete but not fully documented.

Issue: SPR-7655