Updated the gentoo/install sourceable scripts
Moved kernel build/install scripts from kernel/gentoo to gentoo/kernel

* Reason: genkernel is gentoo-specific, and no kernel non
  gentoo-specific scripts are foreseen in the near future
* Updated genkernel-cobalt to use /boot/grub instead of /boot/grub2
Renamed misc/find-hardlinks.sh to misc/find-file-hardlinks
Modified and renamed admin/gentoo/purge-distfiles.sh to admin/gentoo/purge-distfiles
Enhanced and renamed the admin/gentoo/portage-tmpfs.sh to admin/gentoo/emerge-tmpfs
Removed the obsolete admin/gentoo/adduse-package.sh script (obsoleted by admin/gentoo/puse)