Add some unlets before calling :finish
Replace let s:pystr… with call s:rcmd(…)

Makes lines slightly shorter
Do not call mode() with an argument on old Vims
Move powerline setup under :try

Makes it benefit from troubleshooting below
Make troubleshooting routine actually work
Update information about Vim version
Add support for vim.eval('v:version') in test bindings
Merge pull request #1011 from ZyX-I/old-vims

Improve Vim bindings