Alias for version (versionmask) because lots of people use version and then shadow the macro

Signed-off-by: Peter Kriens <peter.kriens@aqute.biz>
[launch] Added -runkeep (was implied but did not work)

And added test case

Signed-off-by: Peter Kriens <peter.kriens@aqute.biz>
Extensive check for imports that point to a black hole (i.e. not exported). Also checks for exporting empty packages.

Also improved tracking the source of the package and added a -check field with options to check.
Merge pull request #732 from pkriens/master

Better check for private package imports, runkeep, versionmask