add a unit test for AsgDataHandles
I should have probably added that when I added the stand-alone version of the ReadHandle, but better late than never…
I added the test to AsgExampleTools so that it can depend on other packages that depend on AsgDataHandles (if necessary), as done for a lot of the tests in Control/AthToolSupport.
I also made some minor fixes in other places while I was at it.
I'm marking this as urgent, just because I'd rather wait until this gets merged before I continue working on the data handles. That way I can add to this test as I add more handles without having to do some fancy git branch acrobatics.