Filter empty elements in cumulative env-update variables.  Thanks to Brian Harring for this patch from bug #151694. (trunk r4741)

svn path=/main/branches/2.1.1/; revision=4933
diff --git a/pym/portage.py b/pym/portage.py
index 7844dc2..6c67ac1 100644
--- a/pym/portage.py
+++ b/pym/portage.py
@@ -509,7 +509,7 @@
 		mylist = []
 		for myconfig in config_list:
 			if var in myconfig:
-				mylist.extend(myconfig[var].split())
+				mylist.extend(filter(None, myconfig[var].split()))
 				del myconfig[var] # prepare for env.update(myconfig)
 		if mylist:
 			env[var] = " ".join(mylist)
@@ -519,7 +519,7 @@
 		mylist = []
 		for myconfig in config_list:
 			if var in myconfig:
-				mylist.extend(myconfig[var].split(":"))
+				mylist.extend(filter(None, myconfig[var].split(":")))
 				del myconfig[var] # prepare for env.update(myconfig)
 		if mylist:
 			env[var] = ":".join(mylist)