rewriteutil: add pointer to help text when rewrite would cause divergence

The evolve extension's version of the hint has this pointer. I missed
it when I moved it to core. This is pretty much the same as
D10723. Turns out I missed two places :(

Differential Revision: https://phab.mercurial-scm.org/D10832

mercurial/rewriteutil.py

@@ -111,7 +111,12 b" def precheck(repo, revs, action=b'rewrit"
                     b'    set experimental.evolution.allowdivergence=True to '
                     b'skip this check'
                 ) % (base_ctx, other_ctx, local_ctx)
-                raise error.InputError(msg)
+                raise error.InputError(
+                    msg,
+                    hint=_(
+                        b"see 'hg help evolution.instability' for details on content-divergence"
+                    ),
+                )
             else:
                 raise error.InputError(
                     msg,

tests/test-amend.t

@@ -241,6 +241,13 b' Cannot cause divergence by default'
   abort: cannot amend 112478962961, as that creates content-divergence with 16084da537dd
   (add --verbose for details or see 'hg help evolution.instability')
   [10]
+  $ hg amend -m divergent --verbose
+  abort: cannot amend 112478962961, as that creates content-divergence with 16084da537dd
+      changeset 112478962961 already has a successor in changeset 16084da537dd
+      rewriting changeset 112478962961 would create "content-divergence"
+      set experimental.evolution.allowdivergence=True to skip this check
+  (see 'hg help evolution.instability' for details on content-divergence)
+  [10]
   $ hg amend -m divergent --config experimental.evolution.allowdivergence=true
   2 new content-divergent changesets
 #endif