rbenv version- test coverage for preferring local over global version file

[richiethomas]

While reading the version.bats file, I noticed that we have the following two specs:

@test "set by local file" {
  create_version "1.9.3"
  cat > ".ruby-version" <<<"1.9.3"
  run rbenv-version
  assert_success "1.9.3 (set by ${PWD}/.ruby-version)"
}

@test "set by global file" {
  create_version "1.9.3"
  cat > "${RBENV_ROOT}/version" <<<"1.9.3"
  run rbenv-version
  assert_success "1.9.3 (set by ${RBENV_ROOT}/version)"
}

These tests ensure that RBENV is able to either a) pull the version from the local .ruby-version file, or b) pull it from the global "${RBENV_ROOT}/version" file. However I notice that there's no test to assert which should be favored over the other, if both exist. In the spirit of "tests as executable documentation", this seems like a useful addition.

This PR adds that additional test.

[mislav]

Super nice. Thank you!