httppeer: make __del__ access to self.urlopener more safe Some errors could in some cases show unfortunate scary and confusing warnings from the httppeer delstructors: abort: nodename nor servname provided, or not known Exception AttributeError: "'httpspeer' object has no attribute 'urlopener'" in <bound method httpspeer.__del__ of <mercurial.httppeer.httpspeer object at 0x106e1f5d0>> ignored``` To mute that, take 7b15dd9125b3 to the next level and use getattr in __del__.

tests: test preserving execbit changes at amending only on execbit platform

tests: put temporary file outside the working directory for test portability test-largefiles-update.t creates temporary file exec-bit.patch inside the working directory for no-execbit platform specific test, but subsequent tests aren't aware of it. On execbit platform, subsequent tests can run successfully, because exec-bit.patch isn't created. But on no-execbit platform, this temporary file makes subsequent tests show "? exec-bit.patch" at each "hg status".