act on some clippy warnings

[mutantbob]

cargo clippy was complaining about a few code constructs, so I tweaked them according to its guidance.

The unit tests have one failiure, but that failure existed in the master branch before I made my changes, and seems unrelated.

[japaric]

bors try

[bors[bot]]

try

Build failed:

• ci

[japaric]

bors merge

[bors[bot]]

Build succeeded:

• ci