clean up tempfile module and rm FIXME

This removes the FIXME suggesting that mkdtemp should rely on the
default umask, because that would make it unusable for making a secure
work area in a world writable directory (have to assume that other users
have created files, directories, hard links, etc. in your directory).
The POSIX mkdtemp function creates a directory with 700 permissions to
avoid this problem.
Implement Ord trait for Timespec
Add a license check to tidy. #4018
testsuite: Update error messages. Unbreak build, I hope
Comments: turn XXXes into FIXMEs
rustc: Make type_names and named_types tables in trans use @str instead of ~str

Cuts down on bad copies (though there are still a few that can go
away once there are impls of push / append / + for @str)
Rename copy_overlapping_memory() to copy_memory()
core: Allow set_buffer_ to be referred to as set-buffer

After a snapshot, we can take out the set_buffer_ version (pipes
syntax exts use it).

As per #4421
xfail-fast the #[main] tests, r=burningtree
Handle region errors where the actual scope is a statement

Prevents a case of "unknown scope, this is a bug".

I judged this too small to review. Closes #4500
Fix the difference method on bit vectors
testsuite: Add license
testsuite: Add xfailed test for #4335
Merge pull request #4546 from alexcrichton/bitv-difference-bug

Fix the difference method on bit vectors
Add Alex Crichton to AUTHORS
repr: represent char values as char literals rather than integers.
add a Set trait and implement it for TreeSet
add a LinearSet type (implementing the Set trait)
Merge pull request #4551 from SimonSapin/char-repr

repr: represent char values as char literals rather than integers.
Add Simon Sapin to AUTHORS