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/chgserver.py

@@ -262,7 +262,7 b' def _loadnewui(srcui, args, cdebug):'
     newui = srcui.__class__.load()
     for a in [b'fin', b'fout', b'ferr', b'environ']:
         setattr(newui, a, getattr(srcui, a))
-    if util.safehasattr(srcui, b'_csystem'):
+    if util.safehasattr(srcui, '_csystem'):
         newui._csystem = srcui._csystem
 
     # command line args