[BUILDR-701] update harmcrest dependancy version

as seen in https://issues.apache.org/jira/browse/BUILDR-701
junit doesn't come with harmcrest dependancy, we have to add it explicitely

without, some people might experience some ClassNotFoundException

it is possible to overide harmcrest version with Buildr.settings.build['harmcrest'],
as it is done with junit or jmock
fix: I had to implement a private const_missing for Harmcrest module
Merge remote-tracking branch 'origin/pr/11'