Record usage for plugins.
Merge pull request #136 from mortardata/jkarn_plugin_usage

Record usage for plugins.
With the new hadoop version I get:

2011-07-28 11:45:31.469 java[77427:1a03] Unable to load realm info from SCDynamicStore

This seems to be the recommended way of fixing it.
Merge pull request #137 from mortardata/jkarn_remove_kerboros_warning

Add fix for kerberos warning per HADOOP-7489
Fix bad error when bundler is not installed
Merge pull request #138 from mortardata/tmillar_bundler_fix

Fix bad error when bundler is not installed