Fixes #169 by throwing an exception if framework.home is specified and you are using subsystems, but you do not specify a subsystem in the value.

This may be a breaking change for a few people but if they are relying on the default behavior, it is inconsistent and they may run into strange bugs, so this is doing them a favor. Hopefully the exception should be clear enough.
Merge pull request #190 from seancorfield/develop

Fixes #169 by throwing an exception if framework.home is specified and y...