changelog: use "vfs.fstat()" instead of "util.fstat()" Just invoking "os.fstat()" with "file.fileno()" doesn't require non ANSI file API, because filename is not used for invocation of "os.fstat()". But "util.fstat()" should invoke "os.stat()" with "fp.name", if file object doesn't have "fileno()" method for portability, and "fp.name" may cause invocation of non ANSI file API. So, this patch makes the constructor of appender class invoke "util.fstat()" via vfs, to encapsulate filename handling.

changelog: use "vfs.rename()" instead of "util.rename()"

vfs: add "open()" for newly added code paths which open files via vfs This patch replaces "open()" by own "__call__()" defined in derived classes at the first invocation, for efficiency of succeeding invocations.