salvaged: track removal-candidates in more cases

If we want to use this information for copy tracing, then we need to be able to
record it.

First we unlock the recording of deletion candidates, and we will actually record
the data in the next changeset.

Differential Revision: https://phab.mercurial-scm.org/D9119

mercurial/merge.py

@@ -781,7 +781,10 b' def manifestmerge('
     if (
         pa not in ([wctx, p2] + wctx.parents())
         and not forcefulldiff
-        and not repo.ui.configbool(b'experimental', b'merge-track-salvaged')
+        and not (
+            repo.ui.configbool(b'experimental', b'merge-track-salvaged')
+            or repo.filecopiesmode == b'changeset-sidedata'
+        )
     ):
         # Identify which files are relevant to the merge, so we can limit the
         # total m1-vs-m2 diff to just those files. This has significant