Replaced some TODO by FIXME

closes #17478
Ignore yet another windows debuginfo test
Teach libsyntax about `if let`
Desugar 'if let' into the appropriate 'match'
Add tests for `if let`
Produce a better error for irrefutable `if let` patterns

Modify ast::ExprMatch to include a new value of type ast::MatchSource,
making it easy to tell whether the match was written literally or
produced via desugaring. This allows us to customize error messages
appropriately.
Move `if let` behind a feature gate
Update based on PR feedback
Add `if let` to the reference
Update after the fall out from the syntax::ptr changes
Temporarily remove the description for the diagnostic E0162

It turns out that adding new diagnostics is causing link failures
in runpass-full-deps tests. Further investigation pending.
auto merge of #17639 : brson/rust/windbg2, r=pcwalton

I swear this is the last step. p=1 please so i can get the bots changed over before the test suite regresses again.
auto merge of #17479 : gamazeps/rust/issue17478, r=alexcrichton

closes #17478
auto merge of #17634 : jakub-/rust/if_let, r=kballard

Continuation of https://github.com/rust-lang/rust/pull/16741.
Use slice syntax instead of slice_to, etc.
Remove the `_` suffix from slice methods.

Deprecates slicing methods from ImmutableSlice/MutableSlice in favour of slicing syntax or the methods in Slice/SliceMut.

Closes #17273.
Put slicing syntax behind a feature gate.

[breaking-change]

If you are using slicing syntax you will need to add #![feature(slicing_syntax)] to your crate.
Review and rebasing changes