pkg/tar: ignore global extended headers
pkg/tar: ignore global extended headers

sgotti/rkt,kinvolk/rkt,sgotti/rkt,nhlfr/rkt,lucasallan/rkt,ybubnov/rkt,euank/rkt,rkt/rkt,s-urbaniak/rkt,coreos/rkt,alban/rkt,kinvolk/rkt,yifan-gu/rkt,akshaykarle/rkt,kinvolk/rkt,dgonyeo/rkt,lucasallan/rkt,achanda/rkt,sstabellini/rkt,akshaykarle/rkt,rkt/rkt,joshix/rkt,jonboulle/rkt,joshix/rkt,squeed/rkt,rkt/rkt,jakon89/rkt,alban/rkt,jjlakis/rkt,Shashwatsh/rkt,yifan-gu/rocket,nhlfr/rkt,intelsdi-x/rkt,euank/rkt,ybubnov/rkt,ybubnov/rkt,monstermunchkin/rkt,monstermunchkin/rkt,jjlakis/rkt,Wilybald/rkt,lucasallan/rkt,achanda/rkt,lucasallan/rkt,yifan-gu/rocket,Wilybald/rkt,squeed/rkt,euank/rkt,shobhit85/rkt,cab105/rkt,sstabellini/rkt,jakon89/rkt,nhlfr/rkt,jonboulle/rkt,alban/rkt,squeed/rkt,Shashwatsh/rkt,coreos/rkt,s-urbaniak/rkt,yifan-gu/rkt,rkt/rkt,Wilybald/rkt,shobhit85/rkt,jjlakis/rkt,Shashwatsh/rkt,sstabellini/rkt,sgotti/rkt,joshix/rkt,Wilybald/rkt,intelsdi-x/rkt,yifan-gu/rkt,achanda/rkt,shobhit85/rkt,joshix/rkt,cab105/rkt,s-urbaniak/rkt,dgonyeo/rkt,monstermunchkin/rkt,cab105/rkt,intelsdi-x/rkt,jakon89/rkt,dgonyeo/rkt,kinvolk/rkt,jonboulle/rkt,akshaykarle/rkt,yifan-gu/rocket,coreos/rkt