If you want to make changes to Spark and run your application with it, you may follow these steps.
1. git clone firstname.lastname@example.org:apache/spark
2. cd spark; build/mvn clean package -DskipTests [...]
3. make local changes
4. build/mvn package -DskipTests [...] (no need to clean again here)
5. bin/spark-submit --master spark://[...] --class your.main.class your.jar
No need to pass in extra --driver-java-options or --driver-extra-classpath as others have suggested. When using spark-submit, the main jar comes from assembly/target/scala_2.10, which is prepared through "mvn package". You just have to make sure that you re-package the assembly jar after each modification.