alpha stable wrt bug #498608

(Portage version: 2.2.8-r1/cvs/Linux x86_64, signed Manifest commit with key 0xC42EB5D6)
Set keepdir /var/lib/flows/ft (bug #483590). Use prune_libtool_files. Set up user/group in pkg_preinst() too.

(Portage version: 2.2.10/cvs/Linux x86_64, signed Manifest commit with key A792A613)
Mask upcoming ~x11-misc/redshift-1.9
Disable split /usr check in build as it breaks when cross-compiling for diff ABIs. We handle this logic ourselves in the ebuild.

(Portage version: 2.2.10/cvs/Linux x86_64, signed Manifest commit with key D2E96200)
x11-misc/redshift: 1.9 (bug #507062)

(Portage version: 2.2.10/cvs/Linux x86_64, signed Manifest commit with key 0x401A1600)