Fixed test output for changed glog (. instead of @)

Issue a warning if "-r ." is used with two working directory parents. Rationale for not aborting instead: The first parent is usually more important as it is the local branch during a merge and commands like 'hg diff' and 'hg diff -r.' behave still identically (except for the warning of course). Added a test for log -r. with one and two parents.

graphlog: Print . instead of @ for working directory parents "." is accepted as an alias for the first working directory parent by -r/--rev

Remove atomicfile class. The interface provided by opener(atomic=True) is inherently unsafe: if an exception is raised in the code using the atomic file, the possibly incomplete file will be renamed to its final destination, defeating the whole purpose of atomic files. To get around this, we would either need some bad hacks involving sys.exc_info (to make sure things work in except: blocks), or an interface to say "file is complete; rename it". This is the exact interface provided by atomictempfile. Since there are no remaining users of the atomicfile class, just remove it.