SPARK-3318: Documentation update in addFile on how to use SparkFiles.get

Rather than specifying the path to SparkFiles we need to use the filename.

Author: Holden Karau <holden@pigscanfly.ca>

Closes #2210 from holdenk/SPARK-3318-documentation-for-addfiles-should-say-to-use-file-not-path and squashes the following commits:

a25d27a [Holden Karau] Update the JavaSparkContext addFile method to be clear about using fileName with SparkFiles as well
0ebcb05 [Holden Karau] Documentation update in addFile on how to use SparkFiles.get to specify filename rather than path
MAINTENANCE: Automated closing of pull requests.

This commit exists to close the following pull requests on Github:

Closes #1922 (close requested by 'JoshRosen')
Closes #1356 (close requested by 'pwendell')
Closes #1698 (close requested by 'mengxr')
Closes #254 (close requested by 'mateiz')
Closes #2135 (close requested by 'andrewor14')
[Spark QA] only check code files for new classes

Look only at code files (`.py`, `.java`, and `.scala`) for new classes.

Should get rid of false alarms like [the one reported here](https://github.com/apache/spark/pull/2014#issuecomment-52912040).

Author: Nicholas Chammas <nicholas.chammas@gmail.com>

Closes #2184 from nchammas/jenkins-ignore-noncode and squashes the following commits:

33786ac [Nicholas Chammas] break up long line
3f91a14 [Nicholas Chammas] rename array of source files
8b82a26 [Nicholas Chammas] [Spark QA] only check code files for new classes