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

@@ -415,7 +415,7 b' def _abssource(repo, push=False, abort=T'
     # type: (localrepo.localrepository, bool, bool) -> Optional[bytes]
     """return pull/push path of repo - either based on parent repo .hgsub info
     or on the top repo config. Abort or return None if no source found."""
-    if util.safehasattr(repo, b'_subparent'):
+    if util.safehasattr(repo, '_subparent'):
         source = urlutil.url(repo._subsource)
         if source.isabs():
             return bytes(source)