…all, --enable-btrfs-separated

Adds Makefile target "install-separated": install all
"btrfs-*.separated" binaries and rename to "btrfs-*". If configured
with --enable-setcap-install, also sets linux capabilities(7) using
setcap(8). If configured with "--enable-setuid-install", sets setuid
bit while installing.

Use --enable-btrfs-separated if you want to build (but not install)
all "btrfs-*.separated" binaries.