Document std::ops.

Added an overview with a 'real' example, as well as toy implementations of all of
the traits.

Closes #9356.
extra: %U support in time::strftime

Fixes #2350
avoid alloca in with_overflow intrinsics

This is pointless, since it's just used to load an `undef` value and
never touched again.
treat uninhabited enums as voidish
make small (<= size_of::<int>()) enums immediate

C-like enums are excluded from this for now, because the code paths
specific to them need to be changed.

    fn foo() -> Option<~int> { Some(~5) }

Before:

    ; Function Attrs: uwtable
    define void @_ZN3foo18hdec6e36682b87eeaf4v0.0E(%"enum.std::option::Option<~int>[#1]"* noalias nocapture sret, { i64, %tydesc*, i8*, i8*, i8 }* nocapture readnone) #0 {
    "function top level":
      %2 = tail call %"enum.std::libc::types::common::c95::c_void[#1]"* @"_ZN2rt11global_heap10malloc_raw17h56c543b77f9b78aY11v0.9$x2dpreE"({ i64, %tydesc*, i8*, i8*, i8 }* undef, i64 8)
      %3 = bitcast %"enum.std::libc::types::common::c95::c_void[#1]"* %2 to i64*
      store i64 5, i64* %3, align 8
      %4 = getelementptr inbounds %"enum.std::option::Option<~int>[#1]"* %0, i64 0, i32 0
      store i64* %3, i64** %4, align 8
      ret void
    }

After:

    ; Function Attrs: uwtable
    define %"enum.std::option::Option<~int>[#1]" @_ZN3foo18h2cbf6557a3143edah4v0.0E({ i64, %tydesc*, i8*, i8*, i8 }* nocapture readnone) #0 {
    "function top level":
      %1 = tail call %"enum.std::libc::types::common::c95::c_void[#1]"* @"_ZN2rt11global_heap10malloc_raw18hb1e9dd1beab35edau11v0.9$x2dpreE"({ i64, %tydesc*, i8*, i8*, i8 }* undef, i64 8)
      %2 = bitcast %"enum.std::libc::types::common::c95::c_void[#1]"* %1 to i64*
      store i64 5, i64* %2, align 8
      %oldret = insertvalue %"enum.std::option::Option<~int>[#1]" undef, i64* %2, 0
      ret %"enum.std::option::Option<~int>[#1]" %oldret
    }
std: Replace num::IntConvertible with {To,From}Primitive
syntax: Add #[deriving(FromPrimitive)] syntax extension

Right now this only works for c-style enums.
syntax: swap from .span_fatal to .span_err in #[deriving(FromPrimitive)]
test: add compile-fail test for #[deriving(FromPrimitive)]
std: Swap {To,From}Primitive to use the 64bit as the unimplemented version

One downside with this current implementation is that since BigInt's
default is now 64 bit, we can convert larger BigInt's to a primitive,
however the current implementation on 32 bit architectures does not
take advantage of this fact.
extra: Add ToBigInt and ToBigUint traits
auto merge of #9677 : thestinger/rust/immediate, r=huonw

C-like enums are excluded from this for now, because the code paths
specific to them need to be changed.

    fn foo() -> Option<~int> { Some(~5) }

Before:

    ; Function Attrs: uwtable
    define void @_ZN3foo18hdec6e36682b87eeaf4v0.0E(%"enum.std::option::Option<~int>[#1]"* noalias nocapture sret, { i64, %tydesc*, i8*, i8*, i8 }* nocapture readnone) #0 {
    "function top level":
      %2 = tail call %"enum.std::libc::types::common::c95::c_void[#1]"* @"_ZN2rt11global_heap10malloc_raw17h56c543b77f9b78aY11v0.9$x2dpreE"({ i64, %tydesc*, i8*, i8*, i8 }* undef, i64 8)
      %3 = bitcast %"enum.std::libc::types::common::c95::c_void[#1]"* %2 to i64*
      store i64 5, i64* %3, align 8
      %4 = getelementptr inbounds %"enum.std::option::Option<~int>[#1]"* %0, i64 0, i32 0
      store i64* %3, i64** %4, align 8
      ret void
    }

After:

    ; Function Attrs: uwtable
    define %"enum.std::option::Option<~int>[#1]" @_ZN3foo18h2cbf6557a3143edah4v0.0E({ i64, %tydesc*, i8*, i8*, i8 }* nocapture readnone) #0 {
    "function top level":
      %1 = tail call %"enum.std::libc::types::common::c95::c_void[#1]"* @"_ZN2rt11global_heap10malloc_raw18hb1e9dd1beab35edau11v0.9$x2dpreE"({ i64, %tydesc*, i8*, i8*, i8 }* undef, i64 8)
      %2 = bitcast %"enum.std::libc::types::common::c95::c_void[#1]"* %1 to i64*
      store i64 5, i64* %2, align 8
      %oldret = insertvalue %"enum.std::option::Option<~int>[#1]" undef, i64* %2, 0
      ret %"enum.std::option::Option<~int>[#1]" %oldret
    }
extra: %G, %g and %V support in time::strftime

Fixes #2350
Check enums in missing_doc lint

Closes #9671
auto merge of #9670 : luisbg/rust/strftime, r=alexcrichton
Package system runtime dependencies into snapshots
Package system runtime dependencies into Windows distribution.
auto merge of #9680 : thestinger/rust/overflow, r=huonw

This is pointless, since it's just used to load an `undef` value and
never touched again.
Highlight line numbers of the lines referred to in the url hash
Prevent source view from wrapping lines