Maven now tests if files generated by the archetypes do actually build
[FLINK-1042] Changed ClassLoader field to be transient.

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.
Remove field0 from CoGroup and Join Operator

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.
Change python2.7 to python in KMeans Quickstart
[FLINK-966] java examples included in packaged example directory

This closes #90
Fix problems with missing files/dependencies with cdh-4 distribution.
Fix legacy names in static webclient contents
Fixes on CDH4 build / Maven improvements:
- 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)
[FLINK-1046] Made sure that Client uses correct user-code class loaders.
Add Sanity Checks for Join/CoGroup with SolutionSet in Record API

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.
Run tests in parallel

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.