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/smartset.py

@@ -137,7 +137,7 b' class abstractsmartset:'
 
         This is part of the mandatory API for smartset."""
         # builtin cannot be cached. but do not needs to
-        if cache and util.safehasattr(condition, b'__code__'):
+        if cache and util.safehasattr(condition, '__code__'):
             condition = util.cachefunc(condition)
         return filteredset(self, condition, condrepr)