Fix issue #8 - transitive dependency exclusions

Accumulate exclusions on dependencies during the breadth-first
traversal of the dependency tree, and take into account "inherited"
exclusions.
Transitive dependencies - unit test

Add a unit test to make sure transitive dependency exclusions work.
Fix packaging types in test data

For testing purposes the POMs do not need to have the packaging type
set to "pom".
Fixed merge conflict
Reworked transitive exclusions