manifest: Download only the packages that will use the host OS

The main idea of this is that if Linux is used to build, the
MacOS packages are not required, this would help faster download the code
and would save space on your hard drive.

note: this does not conflict with nightlies

Change-Id: Iedfcb0c3998991d6a98978cea728e848906c1cc7
Merge branch 'pac-4.4' of git://github.com/PAC-man/pacman into pac-4.4