staticcheck found a couple of minor code cleanup improvements, like
unused variables or an out-of-order defer, mostly in tests.
This patch fixes those problems by making the necessary adjustments.
They're all fairly small, and should not change the logic in any
significant way.
The timestamp string in the t= and x= headers is an "unsigned decimal
integer", but time.Unix takes an int64. Today we parse it as uint64 and
then cast it, but this can cause issues with overflow and type
conversion.
This patch fixes that by parsing the timestamps as signed integers, and
then checking they're positive.
The current .gitignore pattern doesn't work when the private test cases
are a symlink, which can be convenient.
This patch fixes it by changing the pattern to match symlinks as well as
directories.
