Add conditional requirement of importlib for python 2.6/kombu.

eggs.ini

@@ -43,6 +43,7 @@ drmaa = 0.6
 elementtree = 1.2.6_20050316
 Fabric = 1.7.0
 GeneTrack = 2.0.0_beta_1
+importlib = 1.0.3
 kombu = 3.0.12
 lrucache = 0.2
 Mako = 0.4.1

lib/galaxy/queue_worker.py

@@ -5,8 +5,13 @@ reloading the toolbox, etc., across multiple processes.
 
 import logging
 import threading
+import sys
+
 import galaxy.queues
 from galaxy import eggs, util
+if sys.version_info < (2, 7, 0):
+    # Kombu requires importlib to function under Python 2.6.
+    eggs.require('importlib')
 eggs.require('kombu')
 
 from kombu import Connection

lib/galaxy/queues.py

@@ -4,9 +4,14 @@ All message queues used by Galaxy
 
 """
 
+import sys
+
 from galaxy import eggs
 
-eggs.require("kombu")
+if sys.version_info < (2, 7, 0):
+    # Kombu requires importlib to function in Python 2.6.
+    eggs.require('importlib')
+eggs.require('kombu')
 from kombu import Exchange, Queue
 
 ALL_CONTROL = "control.*"