convert: handle past or foreign partial svn copies
Subversion allows revisions to be composed of subparts coming from revisions
before the parent or from other part of the repository. There is no simple
representation for these now, keep the changes but do not track their origins.
% init
% commit
adding base
% qnew mqbase
% qrefresh
% qdiff
diff -r 67e992f2c4f3 base
--- a/base
+++ b/base
@@ -1,1 +1,1 @@
-base
+patched
% qdiff dirname
diff -r 67e992f2c4f3 base
--- a/base
+++ b/base
@@ -1,1 +1,1 @@
-base
+patched