Return a clean build directory from the command line parser.

Otherwise, artifact file paths will not have the expected form
if command-line arguments such ad "-d ." are used.

Change-Id: I1ca3fa4f6167a506a80bf996c6f0f5c97a4e44f8
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
remove superfluous call to removeGeneratedArtifactFromDisk

This is done further up in removeArtifactAndExclusiveDependents
already.

Change-Id: I0a0df223904b8150ac151c905352707c27ced7b8
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
remove unused RuleGraph::removeSiblings

Change-Id: Ia4d61711093f3e3424b2493d8ab39d7524df443c
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>