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/hg.py

@@ -1567,7 +1567,7 b' def verify(repo, level=None):'
 
 def remoteui(src, opts):
     """build a remote ui from ui or repo and opts"""
-    if util.safehasattr(src, b'baseui'):  # looks like a repository
+    if util.safehasattr(src, 'baseui'):  # looks like a repository
         dst = src.baseui.copy()  # drop repo-specific config
         src = src.ui  # copy target options from repo
     else:  # assume it's a global ui object