Cleanup Request mutex usage

[puellanivis]

As I was working on the filexfer PR again, I noticed some use of mutex-protected values outside of holding a mutex, and then not only do all the copies point to the same mutex, but also, because this mutex has to be set, the use of &sftp.Request{} will always generate an invalid structure that will panic.

I realize the pointer to mutex was there so that *r2 = *r would work and not generate an error during go vet that a mutex is being copied, but this design unfortunately creates even more issues than it solved. I tried a bunch of different ways to keep the pointer, but still have &sftp.Request{} not immediately be incurably invalid, but any solutions to this also require a mutex, which is the very problem we’re trying to avoid. We’re then stuck with having to copy values around the mutex. 🙁 A redesign might be necessary to avoid all mutex usage, I am unsure.

Along with cleaning up the mutex usage, I linted a lot of request.go, breaking some lines up, paragraphing, and removing an unused parameter to runLs(), so we can remove some unused path cleanup work, which then removes some imports in both server.go and request.go.

[drakkan]

LGTM, thank you