Fix trigger directory detection code

Patch by Vijay, reviewed by jebllis for CASSANDRA-5826

debian/cassandra.install

@@ -6,6 +6,7 @@ conf/cassandra-rackdc.properties etc/cassandra
 conf/commitlog_archiving.properties etc/cassandra
 conf/cassandra-topology.properties etc/cassandra
 conf/log4j-tools.properties etc/cassandra
+conf/triggers/* etc/cassandra/triggers
 debian/cassandra.in.sh usr/share/cassandra
 debian/cassandra.conf etc/security/limits.d
 debian/cassandra-sysctl.conf etc/sysctl.d

examples/triggers/README.txt

@@ -11,7 +11,7 @@ Installation:
 ============
 change directory to <cassandra_src_dir>/examples/triggers
 run "ant jar"
-Copy build/trigger-example.jar to <cassandra_home>/triggers/
+Copy build/trigger-example.jar to <cassandra_conf>/triggers/
 Copy conf/* to <cassandra_home>/conf/
 Create column family configured in InvertedIndex.properties 
     Example: Keyspace1.InvertedIndex as configured in InvertedIndex.properties

src/java/org/apache/cassandra/triggers/TriggerExecutor.java

@@ -42,7 +42,7 @@ public class TriggerExecutor
 
     private final Map<String, ITrigger> cachedTriggers = Maps.newConcurrentMap();
     private final ClassLoader parent = Thread.currentThread().getContextClassLoader();
-    private final File triggerDirectory = new File(FBUtilities.cassandraHomeDir(), "triggers");
+    private final File triggerDirectory = FBUtilities.cassandraTriggerDir();
     private volatile ClassLoader customClassLoader;
 
     private TriggerExecutor()

src/java/org/apache/cassandra/utils/FBUtilities.java

@@ -69,6 +69,7 @@ public class FBUtilities
     private static ObjectMapper jsonMapper = new ObjectMapper(new JsonFactory());
 
     public static final BigInteger TWO = new BigInteger("2");
+    private static final String DEFAULT_TRIGGER_DIR = "triggers";
 
     private static volatile InetAddress localInetAddress;
     private static volatile InetAddress broadcastInetAddress;
@@ -341,10 +342,16 @@ public class FBUtilities
         return scpurl.getFile();
     }
 
-    public static File cassandraHomeDir()
+    public static File cassandraTriggerDir()
     {
-        String libDir = new File(FBUtilities.class.getProtectionDomain().getCodeSource().getLocation().getPath()).getParent();
-        return new File(new File(libDir).getParent());
+        File triggerDir;
+        if (System.getProperty("cassandra.triggers_dir") != null)
+            triggerDir = new File(System.getProperty("cassandra.triggers_dir"));
+        else
+            triggerDir = new File(FBUtilities.class.getClassLoader().getResource(DEFAULT_TRIGGER_DIR).getFile());
+        if (!triggerDir.exists())
+            throw new RuntimeException("Trigger Directory doesnt exist, please create inside conf.");
+        return triggerDir;
     }
 
     public static String getReleaseVersionString()