Fix eval at mark, more vim-repeat!

Hey! So I'm reaaaly sorry for breaking "eval at mark" when I introduced vim-repeat support (#171) in the latest version (thanks for pointing it out @arthropodSeven! #172).

This patch fixes that issue and hooks up "eval at mark" to vim-repeat (if you have it installed) correctly. So you can use <prefix>emF or whatever then . to repeat that same mark eval! Handy!

Keep those reports flowing if I break things, I hope it's extremely rare (it seems to be) but I do appreciate reports as and when I slip up.