AbstractOpTest: 'uninject' the context properly when cleaning up

When run inside Eclipse, all @Before methods are run before each single
@Test method, and likewise @After methods are run afterwards. This means
that we must take care to clean out all the fields set by
Context#inject(Object), otherwise we will get nasty 'already injected'
errors.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add a test-scope dependency on junit-benchmarks

This framework taps into JUnit and allows to make beautiful graphs and
performance regression tests based on records of previous runs.

To accomodate junit-benchmarks, we have to upgrade the junit dependency
to version 4.11.

For a junit-benchmarks tutorial, see:

	http://labs.carrotsearch.com/junit-benchmarks-tutorial.html

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Turn AddOpBenchmark into a JUnit Benchmark

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Turn the MapperBenchmark into a JUnit Benchmark

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>