Replaced legacy Flayouts Diff commands with Fugitive buit-in analog
I'm using Fugitive to generate diffs now. And it sets ft=git

Before I've managed tempfiles by myself. And set 'diff' type for them.
Now Fugitive does it with 'Git!' command. And Fugitive-generated files
got filetype = 'git'. So, changing autoloaded file name.
Changed some mappings