Rename merge file names
Rename merge file names

Clearer names that reference the HEADs of git: FETCH_HEAD, ORIG_HEAD and
MERGE_HEAD, rather than the names that fugitive uses for them.

tschundler/dotfiles,yzhou61/vim-airline,bling/vim-airline,tschundler/dotfiles,rchicoli/vim-airline,unphased/vim-airline,chrisbra/vim-airline,tschundler/dotfiles