Document for-loop in tutorial section on loops
 Explain container iteration in the loop tutorial

 As suggested by @pnkfelix in #12161, this extends the examples by a for-loop
 that iterates over a string as an example for container iteration.
Adds support for working with URL Paths

It is sometimes useful to parse just the path portion of a URL (path,
query string and fragment) rather than the entire URL.
Register new snapshots

This enables the parser error for `extern mod` => `extern crate` transitions.
extern mod => extern crate

This was previously implemented, and it just needed a snapshot to go through
Update rustdoc testing to test all code blocks

It's too easy to forget the `rust` tag to have a code example tested, and it's
far more common to have testable code than untestable code.

This alters rustdoc to have only two directives, `ignore` and `should_fail`. The
`ignore` directive ignores the code block entirely, and the `should_fail`
directive has been fixed to only fail the test if the code execution fails, not
also compilation.
Fix all code examples
mk: Clean up conditions for including dist.mk
std: clean up ptr a bit
impl fmt::Pointer for &T and &mut T
auto merge of #12282 : cmr/rust/cleanup-ptr, r=huonw
Clean up the Perlin noise benchmark
auto merge of #12270 : bstrie/rust/pnoise, r=huonw

Mostly just style fixes, but also remove a heap allocation and switch to using a buffered writer rather than doing 60,000 `println!`s.
Declare by-value on-stack parameters to be noalias

Function parameters that are to be passed by value but don't fit into a
single register are currently passed by creating a copy on the stack and
passing a pointer to that copy to the callee. Since the copy is made
just for the function call, there are no aliases.

For example, this sometimes allows LLVM to eliminate unnecessary calls
to drop glue. Given

````rust
struct Foo {
    a: int,
    b: Option<~str>,
}

extern {
    fn eat(eat: Option<~str>);
}

pub fn foo(v: Foo) {
    match v {
        Foo { a: _, b } => unsafe { eat(b) }
    }
}
````

LLVM currently can't eliminate the drop call for the string, because it
only sees a _pointer_ to Foo, for which it has to expect an alias. So we
get:

````llvm
; Function Attrs: uwtable
define void @_ZN3foo20h9f32c90ae7201edbxaa4v0.0E(%struct.Foo* nocapture) unnamed_addr #0 {
"_ZN34std..option..Option$LT$$UP$str$GT$9glue_drop17hc39b3015f3b9c69dE.exit":
  %1 = getelementptr inbounds %struct.Foo* %0, i64 0, i32 1, i32 0
  %2 = load { i64, i64, [0 x i8] }** %1, align 8
  store { i64, i64, [0 x i8] }* null, { i64, i64, [0 x i8] }** %1, align 8
  %3 = ptrtoint { i64, i64, [0 x i8] }* %2 to i64
  %.fca.0.insert = insertvalue { i64 } undef, i64 %3, 0
  tail call void @eat({ i64 } %.fca.0.insert)
  %4 = load { i64, i64, [0 x i8] }** %1, align 8
  %5 = icmp eq { i64, i64, [0 x i8] }* %4, null
  br i1 %5, label %_ZN3Foo9glue_drop17hf611996539d3036fE.exit, label %"_ZN8_$UP$str9glue_drop17h15dbdbe2b8897a98E.exit.i.i"

"_ZN8_$UP$str9glue_drop17h15dbdbe2b8897a98E.exit.i.i": ; preds = %"_ZN34std..option..Option$LT$$UP$str$GT$9glue_drop17hc39b3015f3b9c69dE.exit"
  %6 = bitcast { i64, i64, [0 x i8] }* %4 to i8*
  tail call void @free(i8* %6) #1
  br label %_ZN3Foo9glue_drop17hf611996539d3036fE.exit

_ZN3Foo9glue_drop17hf611996539d3036fE.exit:       ; preds = %"_ZN34std..option..Option$LT$$UP$str$GT$9glue_drop17hc39b3015f3b9c69dE.exit", %"_ZN8_$UP$str9glue_drop17h15dbdbe2b8897a98E.exit.i.i"
  ret void
}
````

But with the `noalias` attribute, it can safely optimize that to:

````llvm
define void @_ZN3foo20hd28431f929f0d6c4xaa4v0.0E(%struct.Foo* noalias nocapture) unnamed_addr #0 {
_ZN3Foo9glue_drop17he9afbc09d4e9c851E.exit:
  %1 = getelementptr inbounds %struct.Foo* %0, i64 0, i32 1, i32 0
  %2 = load { i64, i64, [0 x i8] }** %1, align 8
  store { i64, i64, [0 x i8] }* null, { i64, i64, [0 x i8] }** %1, align 8
  %3 = ptrtoint { i64, i64, [0 x i8] }* %2 to i64
  %.fca.0.insert = insertvalue { i64 } undef, i64 %3, 0
  tail call void @eat({ i64 } %.fca.0.insert)
  ret void
}
````
auto merge of #12296 : dotdash/rust/byval_noalias, r=cmr

Function parameters that are to be passed by value but don't fit into a
single register are currently passed by creating a copy on the stack and
passing a pointer to that copy to the callee. Since the copy is made
just for the function call, there are no aliases.

For example, this sometimes allows LLVM to eliminate unnecessary calls
to drop glue. Given

````rust
struct Foo {
    a: int,
    b: Option<~str>,
}

extern {
    fn eat(eat: Option<~str>);
}

pub fn foo(v: Foo) {
    match v {
        Foo { a: _, b } => unsafe { eat(b) }
    }
}
````

LLVM currently can't eliminate the drop call for the string, because it
only sees a _pointer_ to Foo, for which it has to expect an alias. So we
get:

````llvm
; Function Attrs: uwtable
define void @_ZN3foo20h9f32c90ae7201edbxaa4v0.0E(%struct.Foo* nocapture) unnamed_addr #0 {
"_ZN34std..option..Option$LT$$UP$str$GT$9glue_drop17hc39b3015f3b9c69dE.exit":
  %1 = getelementptr inbounds %struct.Foo* %0, i64 0, i32 1, i32 0
  %2 = load { i64, i64, [0 x i8] }** %1, align 8
  store { i64, i64, [0 x i8] }* null, { i64, i64, [0 x i8] }** %1, align 8
  %3 = ptrtoint { i64, i64, [0 x i8] }* %2 to i64
  %.fca.0.insert = insertvalue { i64 } undef, i64 %3, 0
  tail call void @eat({ i64 } %.fca.0.insert)
  %4 = load { i64, i64, [0 x i8] }** %1, align 8
  %5 = icmp eq { i64, i64, [0 x i8] }* %4, null
  br i1 %5, label %_ZN3Foo9glue_drop17hf611996539d3036fE.exit, label %"_ZN8_$UP$str9glue_drop17h15dbdbe2b8897a98E.exit.i.i"

"_ZN8_$UP$str9glue_drop17h15dbdbe2b8897a98E.exit.i.i": ; preds = %"_ZN34std..option..Option$LT$$UP$str$GT$9glue_drop17hc39b3015f3b9c69dE.exit"
  %6 = bitcast { i64, i64, [0 x i8] }* %4 to i8*
  tail call void @free(i8* %6) #1
  br label %_ZN3Foo9glue_drop17hf611996539d3036fE.exit

_ZN3Foo9glue_drop17hf611996539d3036fE.exit:       ; preds = %"_ZN34std..option..Option$LT$$UP$str$GT$9glue_drop17hc39b3015f3b9c69dE.exit", %"_ZN8_$UP$str9glue_drop17h15dbdbe2b8897a98E.exit.i.i"
  ret void
}
````

But with the `noalias` attribute, it can safely optimize that to:

````llvm
define void @_ZN3foo20hd28431f929f0d6c4xaa4v0.0E(%struct.Foo* noalias nocapture) unnamed_addr #0 {
_ZN3Foo9glue_drop17he9afbc09d4e9c851E.exit:
  %1 = getelementptr inbounds %struct.Foo* %0, i64 0, i32 1, i32 0
  %2 = load { i64, i64, [0 x i8] }** %1, align 8
  store { i64, i64, [0 x i8] }* null, { i64, i64, [0 x i8] }** %1, align 8
  %3 = ptrtoint { i64, i64, [0 x i8] }* %2 to i64
  %.fca.0.insert = insertvalue { i64 } undef, i64 %3, 0
  tail call void @eat({ i64 } %.fca.0.insert)
  ret void
}
````
auto merge of #12272 : alexcrichton/rust/snapshot, r=kballard

This notably contains the `extern mod` => `extern crate` change.

Closes #9880
mk: Add prepare.mk

This is a slightly more generic rewrite of install.mk. Currently
used for nothing, but we'll base all the binary distributables off it.
mk: Base the install target on prepare.mk
mk: Fix a dist bug

Fallout from moving doc/ to src/doc
mk: Base the windows dist target on prepare.mk