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/url.py

@@ -190,7 +190,7 b' def _gen_sendfile(orgsend):'
     return _sendfile
 
 
-has_https = util.safehasattr(urlreq, b'httpshandler')
+has_https = util.safehasattr(urlreq, 'httpshandler')
 
 
 class httpconnection(keepalive.HTTPConnection):