tests: demonstrate another failure with in-memory rebase and copies

This is a similar to dd1ab72be983 (test: demonstrate crash with
in-memory rebase and copies, 2019-03-14). The new failure started with
57203e0210f8 (copies: calculate mergecopies() based on pathcopies(),
2019-04-11). It happens in the call to mergemod.update() on
rebase.py:1268 where we call mergemod.update() to graft a node. Since
the mergecopies() rewrite, that calls _related() with the filectx from
the overlaywctx instead of a filectx from the changectx where the file
was last modified. Either should be fine, so I don't think that's
a bug.

Differential Revision: https://phab.mercurial-scm.org/D6357

tests/test-rebase-inmemory.t

@@ -763,6 +763,21 b' Test rebasing a commit with copy informa'
 
   $ cd ..
 
+Test rebasing a commit with copy information
+
+  $ hg init rebase-rename
+  $ cd rebase-rename
+  $ echo a > a
+  $ hg ci -Aqm 'add a'
+  $ echo a2 > a
+  $ hg ci -m 'modify a'
+  $ hg co -q 0
+  $ hg mv a b
+  $ hg ci -qm 'rename a to b'
+  $ hg rebase -d 1 2>&1 | grep '** ProgrammingError'
+  ** ProgrammingError: copydata() called on clean context
+  $ cd ..
+
 Test rebasing when the file we are merging in destination is empty
 
   $ hg init test