Problem:
On devel(nightly) versions, deprecation warnings for hard-deprecated
features are not being displayed. E.g.,
- to be removed in: 0.11
- hard-deprecation since 0.10
- soft-deprecation since 0.9
then 0.10-nightly (0.10.0-dev) versions as well as 0.10.0 (stable)
should display the deprecation warning message.
Solution:
Improve the code and logic on `vim.deprecate()`, and improve
test cases with mocked `vim.version()`.
5a8fe0769c