[meld] Clean up misc.commonprefix slightly

[Kai Willadsen <kaiw src gnome org>]

commit e9b1b60267c8e58161d0889e8a2d3a6ee0fd11b6
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Thu Apr 25 12:03:49 2013 +1000

    Clean up misc.commonprefix slightly

 meld/misc.py |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)
---
diff --git a/meld/misc.py b/meld/misc.py
index f1ff2ea..c1b13ad 100644
--- a/meld/misc.py
+++ b/meld/misc.py
@@ -248,10 +248,9 @@ def write_pipe(command, text, error=None):
 def commonprefix(dirs):
     """Given a list of pathnames, returns the longest common leading component.
     """
-    if not dirs: return ''
-    n = copy.copy(dirs)
-    for i in range(len(n)):
-        n[i] = n[i].split(os.sep)
+    if not dirs:
+        return ''
+    n = [d.split(os.sep) for d in dirs]
     prefix = n[0]
     for item in n:
         for i in range(len(prefix)):