tests/test-diffdir.out

Make hg update more verbose by default (issue12)
(including small changes to revert and backout to not show these stats
 with the exception of backout --merge)

Show update stats (unless -q), e.g.:
K files updated, L files merged, M files removed, N files unresolved

Inform the user what to do after a merge:
(branch merge, don't forget to commit)

Inform the user what to do if a branch merge failed:
There are unresolved merges, you can redo the full merge using:
  hg update -C X
  hg merge Y

Inform the user what to do if a working directory merge failed:
There are unresolved merges with locally modified files.

diff -r acd8075edac9 b
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+123
diff -r acd8075edac9 b
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+123
diff -r acd8075edac9 a
--- a/a
+++ b/a
@@ -0,0 +1,1 @@
+foo
diff -r acd8075edac9 b
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+123