safehasattr: pass attribute name as string instead of bytes

This is a step toward replacing `util.safehasattr` usage with plain `hasattr`.
The builtin function behave poorly in Python2 but this was fixed in Python3.

These change are done one by one as they tend to have a small odd to trigger
puzzling breackage.

mercurial/debugcommands.py

@@ -1278,7 +1278,7 b' def debugdiscovery(ui, repo, remoteurl=b'
     if opts.get(b'old'):
 
         def doit(pushedrevs, remoteheads, remote=remote):
-            if not util.safehasattr(remote, b'branches'):
+            if not util.safehasattr(remote, 'branches'):
                 # enable in-client legacy support
                 remote = localrepo.locallegacypeer(remote.local())
                 if remote_revs: