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/patch.py

@@ -1703,7 +1703,7 b' def reversehunks(hunks):'
 
     newhunks = []
     for c in hunks:
-        if util.safehasattr(c, b'reversehunk'):
+        if util.safehasattr(c, 'reversehunk'):
             c = c.reversehunk()
         newhunks.append(c)
     return newhunks