Fix emacs indentation of multi-line match patterns

Aligns to the same column if the previous line ends in a single '|' (but
not a '||').
Emacs: stay at the correct position when indenting

When indenting a non-blank line, stay at the same cursor position
relative to the content after indenting.
Emacs: indent relative to enclosing block

This changes the indent to calculate positions relative to the enclosing
block (or braced/parenthesized expression), rather than by an absolute
nesting level within the whole file.  This allows things like this to
work:

    let x =
        match expr {
            Pattern => ...
        }

With the old method, only one level of nesting would be added within the
match braces, so "Pattern" would have ended up aligned with the match.

The other change is that multiple parens/braces on the same line only
increase the indent once.  This is a very common case for passing
closures/procs.  The absolute nesting method would do this:

    spawn(proc() {
            // Indented out two indent levels...
    })

whereas the code in this commit does this:

    spawn(proc() {
        // Indented out only one level...
    })
Fix typo in emacs ERT test
rustc: Get rustc compiling with LLVM 3.{3,4} again

The travis builds have been breaking recently because LLVM 3.5 upstream is
changing. This looks like it's likely to continue, so it would be more useful
for us if we could lock ourselves to a system LLVM version that is not changing.

This commit has the support to bring our C++ glue to LLVM back in line with what
was possible back in LLVM 3.{3,4}. I don't think we're going to be able to
reasonably protect against regressions in the future, but this kind of code is a
good sign that we can continue to use the system LLVM for simple-ish things.
Codegen for ARM won't work and it won't have some of the perf improvements we
have, but using the system LLVM should work well enough for development.
travis: Use LLVM 3.3 from the official repos

We can be certain that this version of LLVM will not be changing, so we don't
have to worry about API drift over time.
Fix a pretty printer crash on `/***`.

The pretty printer was treating block comments with more than two
asterisks after the first slash (e.g. `/***`) as doc comments (which are
attributes), whereas in actual fact they are just regular comments.
auto merge of #12586 : chris-morgan/rust/fix-pretty-print-slash-star-star-star-crash, r=alexcrichton

The pretty printer was treating block comments with more than two
asterisks after the first slash (e.g. `/***`) as doc comments (which are
attributes), whereas in actual fact they are just regular comments.
auto merge of #12486 : MicahChalmer/rust/emacs-fixes-round-3, r=brson

I've added details in the description of each comment as to what it does, which I won't redundantly repeat here in the PR.  They all relate to indentation in the emacs rust-mode.

What I will note here is that this closes #8787.  It addresses the last remaining case (not in the original issue description but in a comment), of indenting `match` statements.  With the changes here, I believe every problem described in the issue description or comments of #8787 is addressed.
auto merge of #12581 : alexcrichton/rust/older-llvm, r=brson

In doing so, revert travis to not using a 3.5 build because it seems to be changing enough that it's breaking our C++ glue frequently enough.
fs: use an iterative algorithm for 'mkdir_recursive'

as requested in #6109
fs: use an iterative algorithm for 'rmdir_recursive'