- restores behavior equivalent to Vim compiled without FEAT_MZSCHEME, etc.
(avoids spurious "E492: Not an editor command: EOF") for code such as:
```vim
if 0
perl << EOF
end
EOF
endif
```
see :help script-here
- fixes#1308
- fixes https://github.com/junegunn/vim-plug/issues/111
:diffsplit command used to include some flag value twice. If I was using bitwise
OR it would be OK, but I had addition here. Changed to use bitwise OR.