icasefs: retry directory scan once for already invalidated cache some hg operation (e.g.: qpush) create new files after first dirstate.walk()-ing, and it invalidates _fspathcache for fspath(). then, fspath() will fail to look up specified name in _fspathcache. this causes case preservation breaking, because parts of already normcase()-ed path are used as result at that time. in this case, file creation and writing out should be done before fspath() invocation, so the second invocation of os.listdir() has not so much impact on runtime performance.