Force versions from platform transitively

This started because I witnessed a build failure in eclipse. Those interested can search for "After a gradle cleanEclipse eclipse, and import of spring-xd-extension-batch (which is new) I get a complaint that org.springframework.integration.Message cannot be found" in hipchat and read down from there.

@wilkinsona provided the following fix, which basically applies a version from platform when there is one (not just at first level like the boot plugin does, but across the board)