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/subrepoutil.py

@@ -400,7 +400,7 b' def reporelpath(repo):'
     # type: (localrepo.localrepository) -> bytes
     """return path to this (sub)repo as seen from outermost repo"""
     parent = repo
-    while util.safehasattr(parent, b'_subparent'):
+    while util.safehasattr(parent, '_subparent'):
         parent = parent._subparent
     return repo.root[len(pathutil.normasprefix(parent.root)) :]