Add tpope/vim-repeat compatibility

[wilywampa]

No description provided.

[tommcdo]

Exchange repeats naturally. Can you give more detail about what this is doing?

[wellle]

@tommcdo: I noticed some issues from time to time too. This PR could fix them.

Here's an example:

before

foo
bar

With the surround plugin, type yssb to surround the first lines in parentheses. Pressing . will repeat it to ((foo)). Not press cxx to mark the current line for exchange. Pressing . on the second line should finish the exchange, but it will surround the second line instead:

after

((foo))
(bar)

expected

bar
((foo))

[tommcdo]

Interesting... I'm curious about what's going on here, but for now I'll merge this in.

[wilywampa]

Sure. When calling repeat#set(), vim-repeat saves the value of b:changedtick in g:repeat_tick. The next time . is pressed, vim-repeat checks if b:changedtick has incremented since being saved to g:repeat_tick. If it has, then it assumes that no repeatable action has occurred since repeat#set() was called and it repeats what is in g:repeat_sequence, otherwise it uses Vim's . functionality.

The problem addressed in this PR is that if the action before using Exchange was saved in vim-repeat and then Exchange is used for the first half of an exchange, b:changedtick is not incremented so when the user pressed . vim-repeat fires off g:change_sequence instead of letting Vim repeat the Exchange action. Calling repeat#invalidate() resets g:repeat_tick so that vim-repeat knows it should let Vim do its thing instead of using g:repeat_sequence.