fixes stated grammar for block comments, by adding Kleene '+' in two places.

Closes #1588
fix another subtle bug in comment regex
added defn of non_slash_or_star
auto merge of #5583 : jbclements/rust/docfix-for-block-comment-grammar, r=jbclements

... by adding Kleene '+' in two places, and changing a "non-slash" into "non_slash_or_star".

Closes #1588
tutorial: use "owned box" consistently
Stop building clang

Removing it from the tree is an ordeal and there is no official way
to disable clang via LLVM's Makefiles so this edits the Makefile
in llvm/tools after running configure.
Register snapshots
auto merge of #5615 : brson/rust/noclang, r=brson

r? @graydon

Closes #5403
auto merge of #5623 : brson/rust/snapshot, r=brson
tutorial: improve the owned boxes section
tutorial: improve the managed boxes section
tutorial: add an example of freezing a managed box
auto merge of #5624 : thestinger/rust/tutorial, r=pcwalton
librustc: Remove `fail_unless!`
auto merge of #5628 : brson/rust/assert, r=brson
Add AbiSet and integrate it into the AST.

I believe this patch incorporates all expected syntax changes from extern
function reform (#3678). You can now write things like:

    extern "<abi>" fn foo(s: S) -> T { ... }
    extern "<abi>" mod { ... }
    extern "<abi>" fn(S) -> T

The ABI for foreign functions is taken from this syntax (rather than from an
annotation).  We support the full ABI specification I described on the mailing
list.  The correct ABI is chosen based on the target architecture.

Calls by pointer to C functions are not yet supported, and the Rust type of
crust fns is still *u8.
auto merge of #5631 : brson/rust/abiset, r=brson,brson

Continuing #5421