style fix
allow selecting the MacOSX package manager

Due to the design of the osdeps, package managers and OSes cannot
have the same name. "MacOSX using ports" is now named macos-port and
the port package manager has been renamed into macports. 'MacOSX using
brew' has been renamed to macos-brew and the package manager is still
called 'brew'

I renamed the package manager to retain backward compatibility ('port'
is now added to the OS names if macos-port is selected).