SPARK-2065: Prevent known incompatible plugins from being loaded.
This adds a hardcoded list of plugins (with version number) that are known to cause issues. Plugins on the list are no longer loaded by Spark.
SPARK-2092: Fix Fastpath plugin
A API change in Smack went unnoticed, and caused the FastPath plugin to not load correctly. This commit fixes that, and increases the version number of the plugin.