check-code: separate warnings to avoid repetitive str.startswith

atomictempfile: rewrite docstring to clarify rename() vs. close().

atomictempfile: avoid infinite recursion in __del__(). The problem is that a programmer using atomictempfile directly can make an innocent everyday mistake -- not enough args to the constructor -- which escalates badly. You would expect a simple TypeError crash in that case, but you actually get an infinite recursion that is surprisingly difficult to kill: it happens between __del__() and __getattr__(), and Python does not handle infinite recursion from __del__() well. The fix is to not implement __getattr__(), but instead assign instance attributes for the methods we wish to delegate to the builtin file type: write() and fileno(). I've audited mercurial.* and hgext.* and found no users of atomictempfile using methods other than write() and rename(). I audited third-party extensions and found one (snap) passing an atomictempfile to util.fstat(), so I also threw in fileno(). The last time I submitted a similar patch, Matt proposed that we make atomictempfile a subclass of file instead of wrapping it. Rejected on grounds of unnecessary complexity: for one thing, it would make the Windows implementation of posixfile quite a bit more complex. It would have to become a subclass of file rather than a simple function -- but since it's written in C, this is non-obvious and non-trivial. Furthermore, there's nothing wrong with wrapping objects and delegating methods: it's a well-established pattern that works just fine in many cases. Subclassing is not the answer to all of life's problems.

run-tests: display diff before prompting with --interactive

check-code: warn about naked except clauses

eliminate various naked except clauses

run-tests: fix some missing i/o locks

run-tests: add a lock for console I/O

run-tests: switch timeout handling from alarm to helper thread This should be slightly more portable than signals and be compatible with threaded dispatch.

run-tests: add locking on results struct