rebase: fix bug that prevented dry-run rebases from printing failures

As far as I can tell it should be fine to unconditionally skip
_prepareabortorcontinue if we're in the process of raising an Abort
here.

Differential Revision: https://phab.mercurial-scm.org/D6226

hgext/rebase.py

@@ -949,6 +949,9 b' def _dryrunrebase(ui, repo, action, opts'
         except error.InMemoryMergeConflictsError:
             ui.status(_('hit a merge conflict\n'))
             return 1
+        except error.Abort:
+            needsabort = False
+            raise
         else:
             if confirm:
                 ui.status(_('rebase completed successfully\n'))

tests/test-rebase-dest.t

@@ -214,7 +214,7 b" BUG: cycles aren't flagged correctly whe"
   > |
   > Z
   > EOS
-  abort: no rebase in progress
+  abort: source and destination form a cycle
   starting dry-run rebase; repository will not be changed
   [255]