vim: fix Man when invoked via +MANPAGER
vim: fix Man when invoked via +MANPAGER

`ftplugin/man.vim` bails out too early when the filetype is `man`, so we
temporarily change that while executing it to recover the correct
definition. For now we assume `fixmeman` won't ever be a "real"
filetype.

benknoble/Dotfiles,benknoble/Dotfiles,benknoble/Dotfiles,benknoble/Dotfiles,benknoble/Dotfiles