Fix some clippy warnings in libsyntax#41957

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bors merged 3 commits intorust-lang:masterfrom

llogiq:clippy-libsyntax

May 17, 2017

Commits on May 12, 2017

Fix some clippy warnings in libsyntax
llogiq
committed

Commits on May 15, 2017

adressed comments by @kennytm and @petrochenkov
llogiq
committed

Commits on May 16, 2017

(hopefully) fix pprust error
llogiq
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