Use fchdir when available

[ap]

Exactly what it says on the tin.

[ap]

Hm, I never explained why… You wrote “It’s reliable and faster” in Changes, and those are true, but for me the main reason to do it this way is another one.

Namely, by the time you try to chdir back to where you came from, permissions in some part of the path can have changed, so you cannot go back to where you were before through a path name. This is extremely rare of course, but it can happen. A more common possibility is that the directory may have been renamed or removed – and either a different directory of the same name created there (so you chdir to the wrong place) or not (so your chdir fails). In other words, a path name is not a stable identifier; it is subject to race conditions.

Using fchdir avoids this class of problem.

Sorry I failed to explain myself in the first place – and thanks for accepting the patch anyway!

[eserte]

I created a test which shows one of the advantages of the fchdir operation: #2