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/shelve.py

@@ -516,7 +516,7 b' def mutableancestors(ctx):'
 
 def getcommitfunc(extra, interactive, editor=False):
     def commitfunc(ui, repo, message, match, opts):
-        hasmq = util.safehasattr(repo, b'mq')
+        hasmq = util.safehasattr(repo, 'mq')
         if hasmq:
             saved, repo.mq.checkapplied = repo.mq.checkapplied, False