Certain testing tools (PowerMock, Robolectric) create copies of classes through a custom class loader.
The coverage tool currently won't instrument classes whose names have already been registered as instrumented; this check should also account for different class loaders.
Also, if classes get "reloaded" without a complete ProtectionDomain, they won't be considered for coverage. This situation should also be checked for, so the reloaded classes still get instrumented.
Enhancement: added support for measuring the coverage of classes load…
…ed or reloaded by a custom class loader; closes #149.