diff: add --inverse option Most of the time, one can reverse a diff by swapping the revisions passed with -r but it happens that if you use the global -R, and diff against the tip of the current repo, you can't swap the revisions. One use-case for that is reviewing changes from a bundle before unbundling. One could also pipe the output of `hg diff` to a command line filter that reverses the diff, but that would remove the benefit from color diffs. Therefore, having an option in `hg diff` to reverse a diff is a good thing. The option flag selection was tricky. GNU patch uses -R/--reverse but -R is already used as a global option and --reverse would make --rev ambiguous.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-diff-inverse.out	Thu Nov 05 15:18:56 2009 +0100
@@ -0,0 +1,20 @@
+adding a
+diff -r 2855cdcfcbb7 -r 8e1805a3cf6e a
+--- a/a	Thu Jan 01 00:00:00 1970 +0000
++++ b/a	Thu Jan 01 00:00:00 1970 +0000
+@@ -1,3 +1,3 @@
+-d
+-e
+-f
++a
++b
++c
+diff -r 2855cdcfcbb7 a
+--- a/a
++++ b/a
+@@ -1,5 +1,3 @@
+ d
+ e
+ f
+-g
+-h