rt::io::fs is missing the abilty to change time metadata of files

[alexcrichton]

This is one thing that I forgot to do as part of #10179. From rust you should be able to change the modification times of files (as permitted by the os). Relevant libuv calls are:

• uv_fs_utime
• uv_fs_futime

We should probably have a more rustic name than utime because I personally have no idea what that's implying.

[alexcrichton]

Labeling as an easy bug, but this will require knowledge of following the existing patterns in the uv bindings and bubbling up this information to the rt::io::fs layer. This isn't a super-easy bug, but it also shouldn't be too difficult to get started on!

Right now the representation of times is just a u64, which is sad, but until we get a better choice for representing times in libstd we don't have much choice.

[jeffcutsinger]

So, uh, I went ahead and also implemented this before I realized you were working on it. Sorry I didn't mention it, I just now created a GH account. I noticed what I think is a bug in your implementation. Not sure if it's best to talk about it here or there, but the utime functions in uv are in seconds, whereas the stat function returns milliseconds. I can push up my work and reference it if you want. Otherwise, I'll grab something else.

[alexcrichton]

Ah sorry about that! But you are indeed correct, looks like I need to shift things by a factor of 1000 in a few places, thanks for pointing that out.

Sadly I think that this is thoroughly embedded in my work right now, so it's probably best if I just go ahead with it. Sorry for not saying I was doing this either!