transaction: abstract away the detection of an abandoned transaction

We're about to add another place where this is used, let's not spill this
implementation detail.

mercurial/transaction.py

@@ -59,6 +59,11 b' UNDO_FILES_MAY_NEED_CLEANUP = ['
 ]
 
 
+def has_abandoned_transaction(repo):
+    """Return True if the repo has an abandoned transaction"""
+    return os.path.exists(repo.sjoin(b"journal"))
+
+
 def cleanup_undo_files(report, vfsmap, undo_prefix=b'undo'):
     """remove "undo" files used by the rollback logic
 

mercurial/verify.py

@@ -17,6 +17,7 b' from . import ('
     pycompat,
     requirements,
     revlog,
+    transaction,
     util,
 )
 
@@ -195,7 +196,7 b' class verifier:'
         if not repo.url().startswith(b'file:'):
             raise error.Abort(_(b"cannot verify bundle or remote repos"))
 
-        if os.path.exists(repo.sjoin(b"journal")):
+        if transaction.has_abandoned_transaction(repo):
             ui.warn(_(b"abandoned transaction found - run hg recover\n"))
 
         if ui.verbose or not self.revlogv1: