Use git in manual install instructions to determine the latest release tag, rather than hardcoding it.

Per https://github.com/creationix/nvm/commit/199ba533403b2a3ad615d0a068a05e59e04e522d
All 4 of these test files should be executable.
Fixing these test files that have never been run
copy-packages: ensure that `nvm_version` is also applied to compare the provided version to the current one.
nvm install: Ensure that if a version is not provided, we don't try to shift a nonexistent argument.
nvm install: don't output "additional options" when there are none.