merge with stable

clonebundles: fix typo s/comand/command/

posix: retry on symlink race in checklink Multiple threads might attempt to check links with the same temporary name. This would cause one side to get an EEXIST error and wrongly fail the support check. Here, we simply retry if our temporary name exists.

changegroup: back code change of e7c618cee8df out The previous changeset is a simpler way of fixing issue4934 without changing the spirit of the code. We can remove the dual call to 'delayupdate' but we keep the tests to show that the issue is still fixed.

changegroup: call 'prechangegroup' hook before setting up write delay The 'prechangegroup' interfere with 'delayupdate' logic because it trigger the one time call of 'changelog._writepending' (see issure4934). There is no reason not to call that hook before setting up 'delayupdate' so we move the call a bit earlier to avoid interference.

changegroup: fix the scope of a try finally The try finally is here to ensure we release the just-created transaction. Therefore we should not do half a dozen operations before actually entry the try scope.

encoding: re-escape U+DCxx characters in toutf8b input (issue4927) This is the final missing piece in fully round-tripping random byte strings through UTF-8b. While this issue means that UTF-8 <-> UTF-8b isn't fully bijective, we don't expect to ever see U+DCxx codepoints in "real" UTF-8 data, so it should remain bijective in practice.

encoding: use getutf8char in toutf8b This correctly avoids the ambiguity of U+FFFD already present in the input and similar confusion by working a character at a time.

encoding: handle non-BMP characters in fromutf8b

posix: use getutf8char to handle OS X filename percent-escaping This replaces an open-coded utf-8 parser that was ignoring subtle issues like overlong encodings.