Update one-off scenario for hg. Turns out that 'hg export' doesn't exactly work

if you have multiple commits. Better to use 'hg outgoing -p' to catch
everything that differs from the remote repository.

pep-0374.txt

@@ -477,14 +477,12 @@ hg
   cd trunk
   # Edit some code.
   hg commit -m "Stuff I did"
-  # Create a patch containing the last commit. Use hg export REV: to
-  # export all changes from revision REV (inclusive).
-  hg export tip >> stuff-i-did.patch
+  hg outgoing -p > fixes.patch
   # Upload patch to bugs.python.org
   # Receive reviewer comments
   # Edit some code
   hg commit -m "Address reviewer comments."
-  hg export tip >> additional-fixes.patch
+  hg outgoing -p > additional-fixes.patch
   # Upload patch to bugs.python.org