Fix NullPointerExceptions

Since 5a17627(Make function inputs required), we cannot pass null input
parameters when looking for ops.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix in-place benchmark tests

ParallelMap now only takes in-place functions, and we did not have any
in-place implementation of the "add" op.

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>
TO-UNDO: switch to junit-benchmark 0.8.0-SNAPSHOT

There is a problem with the junit-benchmark: it includes the @Before and
@After methods in the timings:
http://issues.carrot2.org/browse/JUNITBENCH-54

The recommended solution -- uglifying the code as to be unreadable, as
demonstrated here:
https://github.com/carrotsearch/junit-benchmarks/blob/be41b475/src/test/java/com/carrotsearch/junitbenchmarks/TestJUnitHooksWorkAround.java#L20
-- was not acceptable to this developer, who therefore implemented a
workaround relieving users of junit-benchmark of the need for ugly @Rule
incantations: https://github.com/carrotsearch/junit-benchmarks/pull/14

For the moment, let's use junit-benchmark version 0.8.0-SNAPSHOT for
that reason, with the understanding that the developers need to compile
from that pull request locally until a more final solution is found.

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