macvim 7.4-71

Closes #22377.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
(re new) `brew linkapps` defaults to *moving* instead of linking.

This also adds a `--symlink` flag to preserve the old behaviour for those who preferred it; as well
as a `--force` flag for manually upgrading anything Homebrew might have created.