sys-apps/portage: version bump to 2.3.7

sys-apps/portage: version bump to 2.3.7

Fixed bugs:

  #424423 - multilib-strict: disable recursion into subdirectories
  #608880 - eapply_user: combine sort for all dirs
  #610670 - man/portage.5: document -* in profile "packages" files
  #619612 - emerge: warn for --autounmask-continue with --autounmask=n
  #619620 - depgraph: account for binpkg-multi-instance in unused warning
  #619626 - depgraph: prune unnecessary rebuilds for --autounmask-continue
  #622480 - emerge: add --autounmask-keep-keywords option
  #623648 - fuzzy search: weigh category similarity independently
  #625246 - emerge --getbinpkg: https support for If-Modified-Since

Package-Manager: Portage-2.3.7, Repoman-2.3.2