libsyntax/librustc: Allow mut qualifier in patterns.
libsyntax: Get rid of some logic for some obsolete syntax.
Test for mut in ident patterns.
librustc: Don't emit unused mut lint twice.
libsyntax: Get rid of obsolete obsolete warning.
auto merge of #10026 : luqmana/rust/mut-pat, r=pcwalton

Fixes #9792.
Clarify that the SipHash implementation has not be validated for cryptographic purposes.
Update workcache to no longer use Sha1.
Remove MD5 and Sha2. Move Sha1 and support code into librustpkg.
Add a comment to Sha1 that its not suitable for cryptogrpahic uses.
Remove dead code from cryptoutil.rs and remove macro_rules feature flag.
Remove MD4.
Integrate the code in the digest and cryptoutil modules directly into the sha1 module.