This closes #98

This uses the forkCount parameter of surefire/failsafe. This also
changes the JVM memory size for the testing VMs so that more can fit
into memory.

For this to work, NepheleMiniCluster must recognize when it is run in
a parallel testing environment and change ports accordingly. Also
AbstractTestBase and TaskTestBase must prefix temp files with the class
name to prevent name clashes.

This closes #96

This closes #97

This closes #75

This closes #42

We now check whether the key fields specified for the delta iterations
match those specified when joining/coGrouping with the solution set.
This code is more or less copied from the new Java API.

The Scala API uses the Record API underneath so it is also covered.

- remove usages of commons-lang (we use only commons-lang3, as defined in flink-runtime/pom.xml)
- Upgrade maven failsafe to 2.17 so that tests also fail if the test errors (exceptions during execution)
- added new build profile "docs-and-source" that creates javadocs and source attachments. These are usually only needed when releasing (--> speed up the build)

This closes #90

These were added before to force the user to specify at least one key
field. Now, the user is also forced to specify at least one key because
otherwise the call would be ambiguous because of tuple key fields and
expression keys.

Serialization of the `RuntimeStatefulSerializerFactory` fails because the field `ClassLoader loader` is not serializable. The fix makes the field `transient`.

Author: Fabian Hueske <fhueske@apache.org>

Closes #92 from fhueske/StatefulSerializerFactoryFix and squashes the following commits:

c01cc27 [Fabian Hueske] [FLINK-1042] Changed ClassLoader field to be transient.

There are various issues when working with POJOs in the Java API, for
example [1].

This commit squashes the following commmits:

1. Disable tests, which depend on POJO types

2. Replace expression keys with key selector in test

3. PackagedProgramEndToEndITCase used a KMeans variant, which relies on
expression keys to select the field to group on. This commit replaces
this with a key selector.

4. Disable WordCountPOJO test case and package

5. Disables WordCountPOJOITCase, which executes the WordCountPOJO example.
The example code is still included with the source code (with notice
that it is currently not working), but will *not* be packaged as a JAR
anymore.

6. Disable tests, which depend on POJO types (continued)

[1] https://mail-archives.apache.org/mod_mbox/incubator-flink-dev/201407.mbox/%3C53D96049.1060509%40cse.uta.edu%3E

This closes #93.