fix util.copyfile to deal with symlinks

mercurial/util.py

@@ -614,6 +614,13 b' def unlink(f):'
 
 def copyfile(src, dest):
     "copy a file, preserving mode"
+    if os.path.islink(src):
+        try:
+            os.unlink(dest)
+        except:
+            pass
+        os.symlink(os.readlink(src), dest)
+    else:
     try:
         shutil.copyfile(src, dest)
         shutil.copymode(src, dest)