Minor typo change to reflect actual values used.
--- a/hgext/extdiff.py
+++ b/hgext/extdiff.py
@@ -101,7 +101,7 @@ def extdiff(ui, repo, *pats, **opts):
'''use external program to diff repository (or selected files)
Show differences between revisions for the specified files, using
- an external program. The default program used is "diff -Pnru".
+ an external program. The default program used is "diff -Npru".
To select a different program, use the -p option. The program
will be passed the names of two directories to compare. To pass
additional options to the program, use the -o option. These will