Fix for latest Rust
Implement tac (closes #117)
Remove a couple of programs from the to-do list
tac: fix an issue with --separator
Add paste (closes #120)
paste: make MUCH faster and fix a couple bugs
Remove paste from the to-do list
mkdir: improve error handling (closes #121)
stty in progress
allow uppercase variables for du
expand in progress
Fix master by comparing against slices, not ~
Fix master by removing extra crate,
and using max method for comparing floats
Implement uptime

Move utmp struct from users to common/utmpx.rs
du: be dryer when extracting the --max-depth arg.

There's no need to repeat the two checks for `from_str` when we can just
do it preemptively.
du: use multi-line strings and print the actual name, not a literal `du`.
du: remove some clones.
du: make it correct.

Previously, this was handling symlinks wrong (i.e. `du` was following
them, not just looking at them as files). Handling them correctly
requires using `lstat`.

Also, this would abort when reading a file with invalid permissions (or
one that doesn't exist... as a link target of a symlink), rather than
just warning and continuing.

Also, this patch reduces the number of `stat`s done per file to exactly
one (i.e. the minimum).
Fix compilation for latest rustc.

Some warning are still there.

(cherry picked from commit 5c690b33d60725d8ef90c8531adf832f9afd27a8)

Conflicts:
	cp/cp.rs
Add vim formatting comment.

Because otherwise, I can't do any work. ;)

(cherry picked from commit 05d026d0d001f745154c81a131782516581b7be4)