This fixes several Xcode 11 incompatibilities with MacVim, including an
issue where it wasn't inheriting the deployment target correctly to
begin with.
Fix up the macvim package to build again, with the latest snapshot. The
patchfile has been recreated by manually reapplying all of the changes
from the old patchfile, and the other changes in here were figured out
by trial and error (such as the need to unset `LD`).
Also tweak the package to use python37 by default, and add an option to
go back to python27 if desired.
Disable Sparkle so the user isn't prompted to update a readonly package.
MacVim's maintenance has stagnated, so this moves `macvim` to a new maintainer.
Additionally, the `-headerpad_max_install_names` linker flag is passed to
prevent problems when setting the rpaths.
