util: add utility function to skip avoiding file stat ambiguity if EPERM Now, advancing stat.st_mtime by os.utime() is used to avoid file stat ambiguity. But according to POSIX specification, utime(2) with an explicit time information is permitted only for a process with: - the effective user ID equal to the user ID of the file, or - appropriate privileges http://pubs.opengroup.org/onlinepubs/9699919799/functions/utime.html Therefore, just having group write access to a file causes EPERM at applying os.utime() on it (e.g. working on the repository shared by group access permission). This patch adds class filestat utility function avoidamgig() to avoid file stat ambiguity but skip it if EPERM. It is reasonable to always ignore EPERM, because utime(2) causes EPERM only in the case described above (EACCES is used only for utime(2) with NULL).